Abstract:
This semiconductor device ( 10 ) has a heat source element (HSE) and a thermosensor element (TE) on a semiconductor chip (SCH). The profile of the heat source element (HSE) in plan view is recessed, and the depth (y 1 ) of the recessed space (SP) is set to a size from 0.75 to 0.25 times that of the total length (y 0 ). The center part (Tc) of the thermosensor element (TE) is situated in proximity to one side of a linking area (hse 3 ), and is positioned in the space (SP) in such a way that length (y 3 ) is shorter than length (x 31   a ) and length (x 31   b ). In so doing, heat source element temperature detection sensitivity and efficient positioning of the semiconductor elements can be achieved.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to semiconductor devices and to methods for designing them, and more particularly to those provided with a heat source element and a temperature sensing element. 
       BACKGROUND ART 
       [0002]    In a semiconductor device, a heat source element is typically, for example, a bipolar or MIS power transistor through which an electric current of several hundred milliamperes to several amperes passes. A temperature sensing element denotes a semiconductor element that detects the temperature of a semiconductor chip in which a power transistor is formed, in particular the junction temperature of the power transistor itself, and can be an active device, such as a transistor, or a passive device, such as a diode or a resistor. 
         [0003]    A heat source element and a temperature sensing element are adopted in, for example, voltage regulators and DC/DC converters. A high current passes, in a bipolar type, between the collector and emitter of the transistor and, in a MIS type, between the source and drain. Moreover, when a high voltage is applied between the two electrodes, those power transistors consume large amounts of electric power. For example, when a current of 200 mA passes between the source and drain of a MIS transistor, and a voltage of 8 V is applied between the two electrodes, the MIS transistor consumes electric power of 1.6 W. 
         [0004]    As electric power consumption increases, the junction temperature of a power transistor rises, and accordingly the junction temperature of those semiconductor elements which are formed nearby rises. With an abnormally high junction temperature, a semiconductor device is exposed to the risk of deterioration or destruction. To overcome the inconvenience, a temperature sensing element is arranged in a semiconductor chip, particularly near a power transistor, to detect the temperature of the semiconductor chip so that, when a predetermined temperature is reached, the operation of the power transistor and other semiconductor elements, or of the entire semiconductor device, is shut off, thereby to prevent deterioration or destruction of the semiconductor device. 
         [0005]    Patent Document 1 discloses a method for manufacturing a semiconductor integrated circuit device as well as a semiconductor integrated circuit device. A temperature detection circuit portion is provided that detects the temperature of a power MIS transistor in operation and that, when the temperature equals a predetermined value or more, stops the operation of the power MIS transistor. At the center of a power MOSFET region, a temperature detection circuit region is arranged. Purportedly, arranging the temperature detection circuit region at the center of the power MOSFET region, which has the highest temperature when a power IC is in operation, helps enhance temperature detection sensitivity so that power IC protection operation can be performed reliably at a proper time. 
         [0006]    Patent Document 2 discloses a temperature detection circuit and an overheat protection circuit. A diode with temperature dependence is provided in the temperature detection circuit, and an output transistor is arranged so as to surround the diode. Purportedly, the diode with temperature dependence is preferably arranged near the output transistor from the viewpoints of both efficiency and precision, and thus the diode is arranged in a central part of the output transistor (see Patent Document 2, FIG. 5). 
       LIST OF CITATIONS 
     Patent Literature 
       [0007]    Patent Document 1: Japanese Patent Application Publication No. H11-177087 
         [0008]    Patent Document 2: Japanese Patent Application Publication No. 2002-108465 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0009]    Patent Documents 1 and 2 are similar in that a heat source element and a temperature sensing element are provided and that the temperature sensing element is arranged near the heat source element. They also share the reason for arranging the two elements next to each other: to enhance the temperature detection sensitivity of the heat source element (power transistor). 
         [0010]    Nowadays, semiconductor devices themselves are increasingly miniaturized, and accordingly heat source elements are increasingly miniaturized and made increasingly compact. As the area and volume of a heat source decrease, the proportion of a heat source element in a semiconductor chip decreases, and heat generation density increases, making a heat gradient in the semiconductor chip more notable. Against this background, the present inventors studied how best the heat source element and the temperature sensing element disclosed in Patent Documents 1 and 2 could be arranged. As a result, it has been found that, even when semiconductor elements are arranged near each other, simply arranging the two elements close to each other as suggested in Patent Documents 1 and 2 does not achieve sufficient thermal protection. Based on this finding, the present invention aims to provide a semiconductor device, and a method for designing one, that helps enhance the temperature detection precision of a temperature sensing element and that allows efficient arrangement of a thermal protection circuit including the temperature sensing element in a semiconductor chip. 
       Means for Solving the Problem 
       [0011]    According to one aspect of the present invention, a semiconductor device includes a heat source element and a temperature sensing element. As seen in a plan view, the heat source element has a shape defined by: a first side ( 11 ); a second side ( 12 ) that is located on the same line as, but a second distance x 3  away from, the first side ( 11 ) and that extends over a third distance x 2  in a direction away from the first side ( 11 ); a third side ( 13 ) that has the same length as the second distance x 3 ; a fourth side ( 14 ) that connects together one end of the first side ( 11 ) and one end of the third side ( 13 ); a fifth side ( 15 ) that connects together one end of the second side ( 12 ) and the other end of the third side ( 13 ); a sixth side ( 16 ) of which one end is connected to the other end of the first side ( 11 ) and that extends in the same direction as, and has a larger length than, the fourth side ( 14 ), the length being expressed as a length y 0 ; a seventh side ( 17 ) that is connected to the other end of the second side ( 12 ) and of which one end extends in the same direction as, and has a larger length than, the fifth side ( 15 ), the length being expressed as the length y 0 ; and an eighth side ( 18 ) that connects together the other end of the sixth side ( 16 ) and the other end of the seventh side ( 17 ). The eighth side ( 18 ) has a length x 0 , and the temperature sensing element is arranged near the third side ( 13 ). 
         [0012]    According to another aspect of the present invention, a semiconductor device has a heat source element and a temperature sensing element in a semiconductor chip. The heat source element has a U-shape composed of two opposing regions that are located on opposite sides of a space portion and a coupling region that couples together the two opposing regions. The temperature sensing element is arranged in the space portion near the coupling region. 
         [0013]    According to yet another aspect of the present invention, a method for designing a semiconductor device includes: a first step of dividing a U-shaped heat source element having a space portion into three regions and determining the sizes and shapes of the divided regions and of the space portion; a second step of performing a heat distribution simulation with respect to the heat source element and the space portion determined in the first step; a third step of analyzing simulation results performed in the second step; and a fourth step of determining the sizes of the three regions and of the space portion based on simulation results obtained in the third step. 
       Advantageous Effects of the Invention 
       [0014]    A U-shaped heat source element provided in a semiconductor device according to the present invention is set to have a size of a predetermined shape based on a heat distribution simulation. In addition, a space portion having a predetermined shape and size is demarcated, and in the space portion, a temperature sensing element can be arranged efficiently, with enhanced temperature detection sensitivity and precision. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a schematic diagram of a semiconductor device according to the present invention; 
           [0016]      FIG. 2  is an arrangement diagram of the heat source element and the temperature sensing element shown in  FIG. 1 ; 
           [0017]      FIG. 3  is a modified diagram of  FIG. 2 ; 
           [0018]      FIG. 4  is another modified diagram of  FIG. 2 ; 
           [0019]      FIG. 5A ,  FIG. 5B , and  FIG. 5C  are heat distribution simulation diagrams of a semiconductor device according to the present invention; 
           [0020]      FIG. 6A ,  FIG. 6B , and  FIG. 6C  are heat distribution simulation diagram of a semiconductor device according to the present invention; 
           [0021]      FIG. 7  is a temperature gradient diagram of the heat distribution simulation shown in  FIG. 5 ; 
           [0022]      FIG. 8  is a temperature gradient diagram of the heat distribution simulation shown in  FIG. 6 ; 
           [0023]      FIG. 9  is a temperature gradient diagram of the temperature, as determined through simulations, at the central portion Tc of a temperature sensing element TE according to the present invention; 
           [0024]      FIG. 10  is a simulation diagram showing a relationship between consumed electric power and temperature detection sensitivity in a heat source element HSE according to the present invention; 
           [0025]      FIG. 11  is a diagram showing an area ratio between a heat source element HSE and a space portion according to the present invention; and 
           [0026]      FIG. 12  is a diagram showing one example of a specific circuit of a thermal protection circuit TSD arranged in a space portion according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]      FIG. 1  is a schematic diagram of a semiconductor device according to the present invention. The semiconductor device  10  has a heat source element HSE and a temperature sensing element TE formed in a semiconductor chip SCH having a silicon substrate. In the present invention, the heat source element HSE can be a bipolar transistor, a MIS transistor, or the like that acts as a source of heat, like an output transistor or a power transistor used in a voltage regulator, a DC/DC converter, or the like. On the other hand, the temperature sensing element TE can be a semiconductor element, in particular a transistor, a diode, a resistor, or the like, that functions as a temperature sensor provided to monitor the temperature of a heat source element HSE. 
         [0028]    As seen in a plan view, the heat source element HSE is formed in a U shape. The heat source element HSE is composed of opposing regions hse 1  and hse 2  with a comparatively large area and a coupling region hse 3  with a comparatively small area. The opposing regions hse 1  and hse 2  have approximately equal areas. The area of the opposing region hse 1  is expressed as the product of its lengths x 1  and y 0  in directions X and Y respectively. The area of the opposing region hse 2  is expressed as the product of its lengths x 2  and y 0  in directions X and Y respectively. Making lengths x 1  and x 2  equal gives the opposing regions hse 1  and hse 2  equal areas. The two are usually designed to have equal areas. However, the two can be given different areas depending on how various semiconductor elements and bonding pads are located around the heat source element HSE and how semiconductor elements are wired with each other. 
         [0029]    The area of the coupling region hse 3  is expressed as the product of its lengths x 3  and y 2  in directions X and Y respectively. The coupling region hse 3  is located between the opposing regions hse 1  and hse 2  so as to couple together the opposing regions hse 1  and hse 2 . Providing the coupling region hse 3  between the opposing regions hse 1  and hse 2  leaves a space portion SP, where a thermal protection circuit TSD is arranged. The temperature sensing element TE, which functions as a temperature sensor, is a part of the thermal protection circuit TSD. The distance y 3  from a central portion Tc of the temperature sensing element TE to one side of the coupling region hse 3  is designed to be shorter than the shortest distances x 31   a  and x 31   b  from the central portion Tc of the temperature sensing element TE to the opposing regions hse 1  and hse 2 . The reason is as follows: heat conducts to the entire temperature sensing element TE from three directions, namely from the opposing region hse 1 , from the opposing region hse 2 , and from the coupling region hse 3 ; with no heat source element HSE present on the side opposite from the coupling region hse 3 , heat conduction is weaker in direction Y than in direction X. Accordingly, to strengthen heat conduction from the coupling region hse 3 , the distance between one side of the coupling region hse 3  and the central portion Tc of the temperature sensing element TE is reduced. More preferably, the distance from a central portion of the coupling region hse 3  to the central portion Tc of the temperature sensing element TE is made shorter than the distance from central portions of the opposing regions hse 1  and hse 2  to the central portion Tc of the temperature sensing element TE. The aim is as follows: it is surmised that the coupling region hse 3  and the opposing regions hse 1  and hse 2  has highest temperatures at their respective central portions; reducing the distance from the central portion of the coupling region hse 3  to the central portion Tc of the temperature sensing element TE helps increase and quicken heat conduction from the coupling region hse 3  to the temperature sensing element TE. 
         [0030]    Assuming that the length y 0  of the heat source element HSE in direction Y is constant, the area of the coupling region hse 3  is inversely proportional to that of the space portion SP. That is, increasing length y 1  results in reducing length y 2 , and, conversely, increasing length y 2  results in reducing length y 1 . In the present invention, length y 1 , which relates to the space portion SP, is determined with priority over length y 2 , which is related to the coupling region hse 3 . The aim is to secure a sufficiently large space portion SP to arrange the thermal protection circuit TSD in. Determining length y 1  with priority given to the size of the space portion SP affects the area of the coupling region hse 3 . On the other hand, however, the coupling region hse 3  is required to be so large as to conduct sufficient heat to the temperature sensing element TE, and thus needs to have a predetermined or larger area. Thus, there is a limit to giving length y 1  priority. 
         [0031]    The space portion SP also needs to have a predetermined entrance width, that is, a predetermined length x 3 , to arrange the thermal protection circuit TSD in. In addition, the space portion SP needs to have a depth, that is, a length y 1 , sufficiently large not only to secure a sufficient length and area to arrange the thermal protection circuit TSD in but also to allow sufficient heat conduction from the heat source element HSE to the temperature sensing element TE. According to various heat distribution simulations conducted with the present invention, it has been found out that it is preferable that lengths y 0  and y 1  have the relationship 0.25≦y 1 /y 0 ≦0.75. Accordingly, setting such that y 1 /y 0 =0.25 results in making y 2 /y 0 =0.75, and setting such that y 1 /y 0 =0.75 results in making y 2 /y 0 =0.25. How these values are derived will be discussed later. Lengths y 0 , y 1 , and y 2  are specifically such that, for example, y 0 =350 μm and y 1 =y 2 =175 μm, and these lengths are determined on the basis of the current, power, etc. tolerated in the heat source element HSE. 
         [0032]    The lengths of the heat source element HSE and the space portion SP in direction X, namely lengths x 1 , x 2 , and x 3  are determined basically on largely the same basis as lengths y 1  and y 2 . Specifically, lengths x 1 , x 2 , and x 3  are determined on the basis of the current, power, etc. tolerated in the heat source element HSE. For example, they are set such that x 1 =x 2 =250 μm and x 3 =140 μm. Incidentally, lengths x 1  and x 2  are often determined on the basis of the current and power required in the heat source element HSE rather than from the perspective of securing the space portion to accommodate the thermal protection circuit TSD in. 
         [0033]    According to various heat distribution simulations conducted with the present invention, it has been found out that it is preferable that lengths x 0 , x 1 , x 2 , and x 3  have the relationship x 3 ≦x 1 =x 2 ≦3×x 3 . Accordingly, for example, setting such that x 3 =140 μm results in making 140 μm≦x 1 =x 2 ≦420 μm. 
         [0034]    In addition to the heat source element HSE and the thermal protection circuit TSD, another circuit OC is formed in the semiconductor chip SCH. For example, in a case where the semiconductor device  10  includes an LDO (low dropout) regulator, the other circuit OC includes a reference voltage source, a driver for driving an output transistor (heat source element HSE), various control circuits, etc. 
         [0035]      FIG. 2  shows an arrangement of the heat source element HSE and the temperature sensing element TE shown in  FIG. 1 , and particularly shows a positional relationship of the heat source element HSE and the thermal protection circuit TSD including the temperature sensing element TE relative to each other on an enlarged scale. For a detailed discussion of their positional relationship,  FIG. 2  includes more reference signs than  FIG. 1 . The following description proceeds with reference to  FIG. 2 , by use of those reference signs. 
         [0036]    In  FIG. 2 , the heat source element HSE has a U shape. The U shape of the heat source element HSE is composed of a first side  11 , a second side  12 , a third side  13 , a fourth side  14 , a fifth side  15 , a sixth side  16 , a seventh side  17 , and an eighth side  18 . The first and second sides  11  and  12  are located on the same line, a length x 3  apart from each other, and have approximately equal lengths x 1  and length x 2 . The second side  12  extends in a direction away from the direction in which the first side  11  extends. The third side  13  is located a length y 1  away from the first and second sides  11  and  12  in a direction perpendicular to these, and has a length approximately equal to length x 3 . The fourth side  14  extends from end a to end b, and has a length approximately equal to length y 1 . The fifth side  15  extends from end c an end d, and has a length approximately equal to length y 1 . The sixth side  16  is parallel to, but longer than, the fourth side  14 ; it extends from end g to end h, and has a length y 0 . The seventh side  17  is parallel to, but longer than, the fifth side  15 ; it extends from end e to end f, and has a length y 0 . The eighth side  18  is substantially parallel to the first, second, and third sides  11 ,  12 , and  13 ; it extends from end f to end g, and has a length x 0 . Length x 0  equals the sum of the lengths x 1 , x 2 , and x 3 . 
         [0037]    For convenience&#39; sake in terms of description and in particular that of heat distribution simulations described later, the heat source element HSE is divided into three parts, namely the opposing regions hse 1  and hse 2  and the coupling region hse 3 . In the specific embodiment shown in  FIG. 2 , division is achieved by extending the fourth and fifth sides  14  and  15  so as to form two opposing regions and one coupling region; instead, division may be achieved by extending the third side  13  in direction X. Also in that configuration, the heat source element HSE is composed of two opposing regions located at opposite sides of a space portion SP and one coupling region coupling together the two opposing regions. 
         [0038]    In  FIG. 2 , points P 1 , which indicate the central portions of the opposing regions hse 1  and hse 2 , are surmised to be the spots where the heat source element HSE has the highest temperature. The central portion of the coupling region hse 3  is indicated by point P 2 , which too is surmised to be at approximately as high a temperature as at points P 1  provided that coupling region hse 3  has a predetermined or larger size. A central portion of one side of the coupling region hse 3 , namely the third side  13 , is indicated by point P 3 . Point P 3  is the spot on the heat source element HSE which is closest to the central portion Tc of the temperature sensing element. Point P 4  is identical with the central portion Tc of the temperature sensing element TE. The temperature detected at point P 4  is extremely important in estimating the temperature of the heat source element HSE. Point P 5  is located at the entrance of the space portion SP, and is surmised to be the spot at which the space portion SP has the lowest temperature. Accordingly, detecting the temperature at point P 5  is extremely useful in grasping the heat distribution and heat gradient over the enter thermal protection circuit TSD. 
         [0039]    The size and shape of the space portion SP are defined by the opposing regions hse 1  and hse 2  and the coupling region hse 3 . The entrance width of the space portion SP equals length x 3 , and the depth of the space portion SP equals length y 1 . In the space portion SP, the thermal protection circuit TSD is arranged. In particular, the shortest distance y 3  between the central portion Tc of the temperature sensing element TE and the third side  13  is set shorter than the shortest distance x 31   a  between the central portion Tc (point P 4 ) and the fourth side  14  and shorter than the shortest distance x 31   b  between the central portion Tc and the fifth side  15 . The distance from point P 2 , which is the central portion of the coupling region hse 3 , and the central portion Tc (point P 4 ) is set shorter than the distance between point P 1 , which is the central portion of the opposing region hse 1 , and the central portion Tc (point P 4 ). On the opposite side of the temperature sensing element TE from the coupling region hse 3 , no semiconductor device that acts as a heat source is present; thus, heat conduction is weaker in direction Y than in direction X. This inconvenience can be alleviated by the configuration described above. 
         [0040]    In the configuration shown in  FIG. 2 , the space portion SP and the coupling region hse 3  are substantially the same size. Specifically, lengths y 0 , y 1 , and y 2  are such that the ratio y 1 /y 0  equals 0.5, the ratio y 2 /y 0  equals 0.5, and lengths y 1  and y 2  are equal. The entrance width of the space portion SP, that is, length x 3 , equals approximately one-half of length x 1  or x 2 . In this configuration, the coupling region hse 3  occupies one-eighths (12.5%) of the area of the opposing regions hse 1  and hse 2 . The ratio of the area of the space portion SP to the area of the heat source element HSE equals approximately one-ninth (11.1%). 
         [0041]    Moreover, in the configuration shown in  FIG. 2 , the third side  13  is located on line segment P 1 -P 1  that connects between points P 1 , that is, the central portions of the opposing regions hse 1  and hse 2 , so that the temperature sensing element TE is located slightly away from line segment P 1 -P 1 . However, the ratio y 1 /y 0 =0.5 may be set slightly higher, for example at 0.55, so that the temperature sensing element TE is arranged on line segment P 1 -P 1 . 
         [0042]      FIG. 3  shows one modified example of  FIG. 2 .  FIG. 3  differs from  FIG. 2  in the depth of the space portion SP; specifically, the proportion of length y 1  in length y 0  is higher.  FIG. 3  schematically shows a configuration where the ratio of y 1  to y 0 , that is, y 1 /y 0 , is set at 0.75. Increasing the ratio y 1 /y 0  results in increasing the area of the space portion SP; on the other hand, the coupling region hse 3  then has a smaller area. As the thermal protection circuit TSD has an increasingly large circuit scale, it occupies an increasingly large part of the area of the space portion SP. However, as the coupling region hse 3  is increasingly small, the amount of heat that conducts from the coupling region hse 3  to the temperature sensing element TE is increasingly small; it is surmised that, simultaneously, the temperature difference between points P 1 , which are the central portions of the opposing regions hse 1  and hse 2 , and point P 2 , which is the central portion of the coupling region hse 3 , is increasingly large. Accordingly, reducing the area of the coupling region hse 3  results in lowering the temperature detection sensitivity of the temperature sensing element TE, and this cannot be said preferable. 
         [0043]    Irrespective of the area of the space portion SP, the shortest distance y 3  between the central portion Tc (point P 4 ) of the temperature sensing element TE and the coupling region hse 3  is set shorter than the shortest distances x 31   a  and x 1   b  between the central portion Tc and the opposing regions hse 1  and hse 2 . The distance between the central portion Tc and point P 2  is set shorter than the distance between the central portion Tc and point P 1 . In this way, it is possible to correct for the difference in heat conduction between across the coupling region hse 3  and across the opposing regions hse 1  and hse 2 . 
         [0044]    Setting the ratio y 1 /y 0  of length y 1  to length y 0  at 0.75 gives the space portion SP a large depth, but gives the coupling region hse 3  a reduced area due to the ratio y 2 /y 0  of length y 2  to length y 0  being 0.25. 
         [0045]      FIG. 4  shows another modified example of  FIG. 2 .  FIG. 4  differs from  FIGS. 2 and 3  in the depth of the space portion SP; specifically the proportion of length y 1  in length y 0  is lower.  FIG. 4  schematically shows a configuration where the ratio y 1 /y 0  of y 1  to y 0  is set at 0.25. Reducing the ratio y 1 /y 0  results in reducing the area of the space portion SP; on the other hand, the heat source element HSE then has a larger area. As the thermal protection circuit TSD has an increasingly small circuit scale, an increasingly small area is required in the space portion SP. However, too small an area of the space portion SP makes it impossible to arrange the thermal protection circuit TSD amply in the space portion SP. It is generally surmised that enlarging the coupling region hse 3  will pose no problem from the perspective of heat conduction. On the other hand, the distance from point P 2 , which is the central portion of the coupling region hse 3 , to the central portion (point P 4 ) of the temperature sensing element TE will then be larger, and thus it is also surmised that the efficiency of heat conduction from the coupling region hse 3  will be lower. 
         [0046]    Also in  FIG. 4 , irrespective of the area of the space portion SP, the shortest distance y 3  between the central portion Tc (point P 4 ) of the temperature sensing element TE and the coupling region hse 3  is set shorter than the shortest distances x 31   a  and x 31   b  between the central portion Tc and the opposing regions hse 1  and hse 2 . The distance between the central portion Tc and point P 2  is set shorter than the distance between the central portion Tc and point P 1 . In this way, it is possible to suppress a difference in heat conduction between across the coupling region hse 3  and across opposing regions hse 1  and hse 2 . 
         [0047]    Setting the ratio y 1 /y 0  of y 1  to y 0  at 0.25 gives the space portion SP a small depth, but gives the coupling region hse 3  an increased area due to the ratio y 2 /y 0  of y 2  to/y 0  being 0.75. 
         [0048]      FIGS. 5A to 5C  show the results of heat distribution simulations with the U-shaped heat source element HSE and the space portion SP shown in  FIGS. 1 to 4 . The simulations were performed with the U-shaped heat source element HSE divided into three parts; it was divided, as shown in  FIGS. 1 and 2 , along direction X into three parts, namely two opposing regions hse 10  and hse 20  and one coupling region hse 30 . It may additionally be divided also along direction Y into a total of three regions, namely two coupling regions with a comparatively small area and one opposing region with a comparatively large area. In either case, one feature of heat distribution simulations according to the present invention is that a U-shape is divided into two opposing regions and one coupling region. 
         [0049]    In the heat distribution simulations, CAE (computer-aided engineering) was used. The results of the heat distribution simulations were derived from, not only the size of the semiconductor chip SCH of the semiconductor device  10  and the size of the heat source element HSE, but also constant values, such as thermal conductivity coefficient [W/m·° C.], density [kg/m 3 ], and specific heat, of so-called component materials such as the leadframe on which the semiconductor device  10  was mounted, the die-bonding material, the wire, the sealing resin, etc. 
         [0050]    In the heat distribution simulations according to the present invention, a silicon semiconductor chip SCH was used which had a size in the range, for example, from 1.0 mm×1.0 to 1.4 mm×1.4 mm. The heat source element HSE had an area that was 9% to 33% of the area of the entire semiconductor chip SCH. 
         [0051]    In  FIGS. 5A to 5C , the opposing regions hse 10  and hse 20  had lengths x 10  and x 20  of, for example, 250 μm, and both had a length y 0  of 350 μm. The coupling region hse 30  had a length x 30  of 110 μm, and was configured such that a distance (separation width) of 15 μm was left between the coupling region hse 30  and the opposing regions hse 10  and hse 20 , that the coupling region hse 30  was separated from the opposing region hse 10  and from the opposing region hse 20 , and that the opposing regions hse 10  and hse 20  were separated from each other. 
         [0052]      FIGS. 5A to 5C  differ in lengths y 1  and y 2 . In all of  FIGS. 5A to 5C , length y 0 , which is the sum of lengths y 1  and y 2 , is constant. 
         [0053]    In the heat distribution simulations according to the present invention, the electric power consumed in the heat source element HSE was so adjusted that the maximum temperature of the semiconductor chip SCH was 250° C. Specifically, the heat source element HSE was supplied with an electric power of 30 W. A maximum temperature of 250° C. is not one that is tolerated in semiconductor devices of this type, but was simply for the sake of simulation. An electric power consumption of 30 W, too, deviates from a normal use condition. Simulations performed under such a condition that greatly deviates from a normal use condition are considered to be useful to predict unexpected behavior and to estimate specific values of an actual heat distribution. 
         [0054]      FIG. 5A  schematically shows a configuration where lengths y 1  and y 2  were equal. With lengths y 1  and y 2  equal, the area of the space portion SP was approximately equal to that of the coupling region hse 30 . In this configuration, the temperature at points P 1 , which were the central portions of the opposing regions hse 10  and hse 20 , and the temperature at point P 2 , which was the central portion of the coupling region hse 30 , were both 250° C., thus with no difference between the spots. The temperature at point P 3 , which was in the part of the coupling region hse 30  opposite the temperature sensing element TE (unillustrated), was about 230° C., and the temperature at point P 4 , which was the central portion of the temperature sensing element TE, was about 200° C. The temperature at point P 5 , which was located at an end of the space portion SP, was about 150° C. Thus, the temperature difference between points P 1  and P 2  with the highest temperature and point P 5  was about 100° C., and the temperature difference between opposite ends of the space portion SP was about 80° C. This means that, when the thermal protection circuit TSD was arranged in the space portion SP, a temperature difference of approximately 80° C. raised between elements arranged at points P 3  and P 5  in the space portion SP. A temperature difference of 80° C. was one that arose when the temperature at points P 1  and P 2  reached 250° C. Assuming that the tolerated temperature at points P 1  and P 2  is, for example, 150° C., the temperature difference is surmised to be about 50° C. instead of 80° C. 
         [0055]      FIG. 5B  schematically shows a configuration where, compared with  FIG. 5A , the space portion SP was given a larger area and the coupling region hse 30  was given an accordingly smaller area. Specifically, in this configuration, length y 1  equaled two-thirds (67%) of length y 0 , and the length y 2  of the coupling region hse 30  was one-third (33%) of length y 0 . In this configuration, when the temperature at point P 1  was 250° C., the temperature at point P 2 , which was the central portion of the coupling region hse 30  was slightly lower, specifically about 240° C. The temperature at point P 3  was about 220° C., and the temperature at point P 4  was about 210° C. The temperature distribution at points P 3  and  4  was largely the same as in  FIG. 5A . 
         [0056]    The reason that the temperature distribution at points P 3  and P 4  in  FIG. 5B  was largely the same as in  FIG. 5A  is surmised to be that, at those points, heat conduction from the opposing regions hse 10  and hse 20  and heat conduction from the coupling region hse 30  jostled each other, with the opposing regions hse 10  and hse 20  having a stronger power to dominate than the coupling region hse 30 . The temperature at point P 5  was about 140° C., largely the same as in  FIG. 5A . The reason is surmised to be that, at point P 5 , which was far away both from the points P 1 , which were the central portions of the opposing regions hse 10  and hse 20 , and from the point P 2 , which was the central portion of the coupling region hse 30 , the power to dominate heat conduction was weak. 
         [0057]      FIG. 5C  schematically shows a configuration where, compared with  FIG. 5B , the space portion SP was given a still larger area and the heat source element HSE was given an accordingly smaller area. Specifically, length y 1  was nine-tenths of length y 0 , and the length y 2  of the coupling region hse 30  was one-tenth of length y 0 . In this configuration, when the temperature at points P 1  and P 2  was 250° C., the temperature at points P 2  and P 3 , which was the central portion of the coupling region hse 30 , was about 200° C. The temperature at point P 4 , which was the central portion Tc of the temperature sensing element TE, was about 190° C., and thus was about 20° C. lower than in  FIG. 5B . In any case, the temperature at the central portion Tc of the temperature sensing element TE was about 60° C. different from the maximum temperature of 250° C., indicating lower temperature detection sensitivity than in  FIGS. 5A and 5B . The reasons for lower temperature detection sensitivity are surmised to be a smaller area (volume) of the coupling region hse 30  resulting in weaker heat conduction to the temperature sensing element TE and a longer distance from the points P 1 , which are the central portions of the opposing regions hse 10  and hse 20 , to the temperature sensing element TE. 
         [0058]    Like  FIGS. 5A to 5C ,  FIGS. 6A to 6C  show the results of heat distribution simulations with the U-shaped heat source element HSE shown in  FIGS. 1 to 4 . The electric power that was applied to the entire heat source element HSE was assumed to be 30 W as in  FIGS. 5A to 5C . 
         [0059]    In  FIGS. 6A to 6B , the lengths x 12  and x 22  of the opposing regions hse 12  and hse 22  both equaled 330 μm, length y 0  equaled 350 μm, the length x 32  of the coupling region hse 32  equaled 110 μm, and a configuration was adopted where a distance of 15 μm was left between the coupling region hse 32  and the opposing regions hse 12  and hse 22 , the coupling region hse 32  was separated from the opposing region hse 12  and from the opposing region hse 22 , and the opposing regions hse 12  and hse 22  were separated from each other. Accordingly, in  FIGS. 6A to 6C , the lengths x 12  and x 22  of the opposing regions hse 12  and hse 22  equaled three times the length x 32  of the coupling region hse 32 . This three-fold size differed from the approximately two-fold size shown in  FIGS. 5A to 5C . 
         [0060]    Among  FIGS. 6A to 6C , lengths y 1  and y 2  differ. As in  FIGS. 5A to 5C , in all of  FIGS. 6A to 6C , length y 0 , which is the sum of lengths y 1  and y 2 , is constant. 
         [0061]      FIG. 6A  shows a configuration where the space portion SP was given a comparatively small area. The ratio y 1 /y 0  of y 1  to y 0  equaled 0.25, and the ratio y 2 /y 0  of y 2  to y 0  equaled 0.75. With this configuration, heat distribution simulations with the heat source element HSE and the space portion SP revealed that, when the temperature at point P 1  was highest, specifically 250° C., the temperature at point P 2  also was 250° C. The temperature at point P 3  then was about 240° C., and the temperature at point P 4 , which was the central portion Tc of the temperature sensing element TE, was about 220° C. The temperature at point P 5  was about 210° C., and thus exhibited a temperature difference of about 40° C. from the temperature at point P 1 , indicating a large difference from what is shown in  FIGS. 5A to 5C . 
         [0062]      FIG. 6B  shows a configuration where the space portion SP was given a still larger area than in  FIG. 6(A) . The ratio y 1 /y 0  of y 1  to y 0  equaled 0.5, and the ratio y 2 /y 0  of y 2  to y 0  equaled 0.5. With this configuration, heat distribution simulations with the heat source element HSE and the space portion SP revealed that, when the temperature at point P 1  was highest, specifically 250° C., the temperature at point P 2  also was 250° C. The temperature at point P 3  then was about 240° C., and the temperature at point P 4  was about 230° C. Thus, the temperature at point P 4 , which was the central portion Tc of the temperature sensing element TE, was about 20° C. lower than the temperature at point P 1 . The temperature at point P 5  was about 200° C. 
         [0063]    In the configuration in  FIG. 6B , the area of the space portion SP and the area of the coupling region hse 32  are set approximately equal. Then, the distance from point P 1  to point P 4 , that is, the distance from the central portions of the opposing regions hse 12  and hse 22  to the central portion (point P 4 ) of the temperature sensing element TE is shortest. This shortest distance is shorter than that shown in  FIG. 6A . Accordingly, the heat with the highest temperature is efficiently conducted to the temperature sensing element TE, and thus it is surmised that even part of the space portion SP is held at a high temperature. 
         [0064]      FIG. 6C  shows a configuration where the area of the space portion SP was still larger than in  FIG. 6B . The ratio y 1 /y 0  of y 1  to y 0  equaled 0.75, and the ratio y 2 /y 0  of length y 2  to length y 0  equaled 0.25. With this configuration, heat distribution simulations with the heat source element HSE and the space portion SP revealed that, when the temperature at point P 1  was highest, specifically 250° C., the temperature at point P 2  was about 240° C. Then the temperature at points P 3  and P 4  was about 230° C. That is, the temperature at point P 4 , which was the central portion Tc of the temperature sensing element TE, exhibited a temperature difference of about 20° C. from the highest temperature. Thus, as compared with  FIG. 6C , the temperature difference between the highest temperature of the heat source element HSE and the temperature detected by the temperature sensing element TE was approximately the same. 
         [0065]    In the structures of the heat source element HSE shown in  FIGS. 6A to 6C , as in those shown in  FIGS. 5A to 5C , the heat source element HSE is divided into three parts, namely two opposing regions and one coupling region. Simulations may also be performed with a heat source element HSE having a division structure different from those shown in  FIGS. 6A to 6C , for example with a structure like the one shown in  FIG. 2  where the third side  13  is extended up to the sixth and seventh sides  16  and  17  to achieve division into three parts, namely two opposing regions and one coupling region. Also with such a configuration, the two opposing regions are arranged on opposite sides of the space portion SP, and the coupling region is formed so as to couple together the two opposing regions. 
         [0066]      FIG. 7  is a temperature gradient diagram showing the results of the heat distribution simulations shown in  FIG. 5  from a different perspective. In  FIG. 7 , along the horizontal axis are taken points P 1  to P 5 , and along the vertical axis is taken the temperature difference from the highest temperature, that is, the temperature at point P 1 . As a parameter of a heat distribution, the depth of the space portion SP, that is, the ratio y 1 /y 0 , is taken, and three values, namely y 1 /y 0 =0.90, y 1 /y 0 =0.67, and y 1 /y 0 =0.50, are adopted. 
         [0067]    In  FIG. 7 , point P 1  indicates the central portions of the opposing regions hse 10  and hse 20  The temperature at point P 1  was found to be about 250° C. irrespective of the value of the parameter. 
         [0068]    Point P 2  corresponds to the central portion of the coupling region hse 30 . The temperature at point P 2  differed slightly from that at point P 1 : it exhibited the smallest temperature difference when the ratio y 1 /y 0  equaled 0.5, the temperature difference then being 0° C., and was then equal to the temperature at point P 1 ; it exhibited the largest temperature difference when ratio y 1 /y 0  equaled 0.9, that is, when the space portion SP was given the largest area and the coupling region hse 30  was given the smallest area throughout the simulations. The temperature at point P 2  then was about 50° C. lower than that at point P 1 . 
         [0069]    Point P 3  corresponds to a part of one side of the coupling region hse 30 ; that is, it is the spot that corresponds to the end of the depth of the space portion SP and that is surmised to have the highest temperature in the space portion SP. Like point  2 , point  3  exhibited the smallest temperature difference when the ratio y 1 /y 0  equaled 0.5, the temperature difference then being about 20° C.; it exhibited the second smallest temperature difference when the ratio y 1 /y 0  was 0.67; it exhibited the largest temperature difference when the ratio y 1 /y 0  equaled 0.9, the temperature difference then being about 50° C. 
         [0070]    Point P 4  corresponds to the central portion Tc of the temperature sensing element TE. Point P 4  was 30 μm to 60 μm away from point P 3 , and had a temperature that was about 20° C. lower than that at point P 3 . However, no large temperature difference was observed between when the ratio y 1 /y 0  equaled 0.5 and when the ratio y 1 /y 0  equaled 0.67. However, compared with the temperatures observed at those times, a temperature difference of about 20° C. was observed when the ratio y 1 /y 0  equaled 0.9. However, the temperature difference at point P 4  was reduced compared with that at point P 3 . 
         [0071]    Point P 5  corresponds to a so-called entrance of the space portion SP, and is surmised to be the spot where the temperature is lowest in the space portion. Despite that, the simulation results revealed a temperature difference of about 110° C. when the ratio y 1 /y 0  was in the range from 0.5 to 0.9. However, the temperature difference at point P 5  was reduced compared with that at point P 2 . Incidentally, the characteristics shown in  FIG. 7  can be interpreted as indicating that no large temperature difference was observed among the temperatures at different points when the ratio y 1 /y 0  was in the range firm 0.67 to 0.5. While no simulations were performed with the ratio y 1 /y 0  less than 0.5, it is surmised that characteristics similar to those observed when ratio y 1 /y 0  equaled 0.67 will be observed. 
         [0072]      FIG. 8  is a temperature gradient diagram showing the results of the heat distribution simulations shown in  FIGS. 6A to 6C  from a different perspective. In  FIG. 8 , along the horizontal axis are taken points P 1  to P 5 , and along the vertical axis is taken the temperature difference from the highest temperature, that is, the temperature at point P 1 . As a parameter of a heat distribution, the depth of the space portion SP, that is, the ratio y 1 /y 0 , is taken, and three values, namely y 1 /y 0 =0.75, y 1 /y 0 =0.50, y 1 /y 0 =0.25, are adopted. 
         [0073]    In  FIG. 8 , point P 1  indicates the central portions of the opposing regions hse 12  and hse 22 . The temperature at point P 1  was about 250° C. irrespective of the value of the parameter. Compared with the characteristics shown in  FIG. 7 , those shown in  FIG. 8  exhibit smaller temperature differences, indicating that preferable results were obtained. It was also found that, as the depth of the space portion SP was varied, the temperatures at different points varied with approximately the same tendency as in  FIG. 7 . Specifically, the temperature difference was smallest when the ratio y 1 /y 0  equaled 0.5, and when the ratio was higher or lower, the temperature differences between point P 1  and the other points tended to increase. However, compared with  FIG. 7 , the temperature differences at different points were smaller in  FIG. 8 , the absolute value of each temperature difference being reduced to approximately one-half. 
         [0074]    Point P 2  corresponds to the central portion of the coupling region hse 32 . The temperature at point P 2  remained substantially the same irrespective of the ratio y 1 /y 0 , and approximately equaled the highest temperature, namely 250° C. 
         [0075]    Point P 3  corresponds to a part of one side of the coupling region hse 32 ; that is, it is the spot that corresponds to the end of the depth of the space portion SP and that is surmised to have the highest temperature in the space portion SP. The temperature difference at point P 3  remained substantially the same irrespective of the depth of the space portion SP, and was approximately 240° C. 
         [0076]    Point P 4  corresponds to the central portion Tc of the temperature sensing element TE. Point P 4  was 30 μm to 60 μm away from point P 3 , and had a temperature that was about 10° C. lower than that at point P 3 . However, a temperature difference of about 10° C. was observed between when the ratio y 1 /y 0  equaled 0.5 and when the ratio y 1 /y 0  equaled 0.25 or 0.75, the temperature difference thus being approximately the same as that at point P 3 . 
         [0077]    Point P 5  corresponds to the entrance of the space portion SP, and is surmised to be the spot where the temperature is lowest in the space portion. Despite that, the simulation results revealed a temperature in the range of 0.25≦y 1 /y 0 ≦0.75, about 50° C. lower than the highest temperature. However, the temperature at point P 5  exhibited a temperature difference that is one-half of that in  FIG. 7 , that is, a greatly reduced temperature difference from the temperature at point P 1 . 
         [0078]    To summarize,  FIG. 8  reveals the following: giving the opposing regions hse 12  and hse 22  an area (volume) larger than that of the coupling region hse 32  results in a smaller temperature gradient in the space portion SP, which is preferable in arranging the temperature sensing element TE there. 
         [0079]      FIG. 9  is a temperature gradient diagram that plots the temperatures at point P 4  shown in  FIGS. 7 to 8 , in particular the temperature differences from the highest temperature of 250° C. It is needless to say that point P 4  corresponds to the central portion Tc of the temperature sensing element TE and is a spot that is especially important for the monitoring of the temperature of the heat source element HSE. Specifically, it is possible to obtain increasingly high temperature detection sensitivity the closer the temperature at point P 4  is to the temperature at point P 1 . 
         [0080]      FIG. 9  gives two plots for different values as a parameter. One depicts a case where, as shown in  FIGS. 5A to 5C , the ratio of the length x 10  (x 20 ) to the length x 30  of the coupling region hse 30  in direction X, that is, x 10  (x 20 )/x 30 , equaled 2; the other depicts a case where, as shown in  FIG. 6 , the ratio of the length x 12  (x 22 ) to the length x 32  of the coupling region hse 32  in direction X, that is, x 12  (x 22 )/x 32 , equaled 3. In short, temperature detection sensitivity is compared between cases where the opposing regions were given a width that was twice and three times, respectively, that of the coupling region. 
         [0081]      FIG. 9  reveals that giving the opposing regions a width larger than that of the coupling region results in a smaller temperature difference and higher temperature detection sensitivity. This tendency remained the same irrespective of the ratio (y 1 /y 0 ) that indicates the depth of the space portion SP. For example, when the ratio y 1 /y 0  equaled 0.5, the temperature difference was about 20° C. with the triple width and about 40° C. with the double width, the temperature difference approximately doubling between the two cases. 
         [0082]      FIG. 9  also reveals that it is preferable that the ratio y 1 /y 0 , which indicates the depth of the space portion SP, be close to a ratio y 1 /y 0  of 0.5, specifically in a range, for example, from 0.25 to 0.75. 
         [0083]      FIG. 9  shows plots for cases where the opposing regions hse 10  and hse 20  or hse 12  and hse 22  were given a width that is twice or three times, respectively, the width of the coupling region hse 30  or hse 32 . It is however surmised that the present invention will provide a similar effect not only with the double or triple width but even with an equal width, that is, even when the opposing regions have the same width as the coupling region. With reference back to  FIGS. 5A to 5C , as will be understood from  FIG. 5C , heat conduction to the space portion SP is insufficient because of a long distance from the central portions (points P 1 ) of the opposing regions hse 10  and hse 20 . However, it is understood that increasing the area of the coupling region hse 30  until it has a certain size as shown in  FIG. 5A  results in a rise in the temperature in the space portion SP. This state, seen from a different perspective, means that the coupling region hse 30  is dominant in heat conduction to the space portion SP. In this state, the width of the coupling region hse 30  is one-half of that of the opposing regions hse 10  and hse 20 . This can be interpreted to indicate that giving the opposing regions hse 10  and hse 20  the same width as the coupling region hse 30  will provide a similar effect. 
         [0084]    In the semiconductor device  10  according to the present invention, the heat source element HSE is formed in a U-shape and, to provide the space portion SP with a predetermined size, is divided into three regions classified into two opposing regions and one coupling region. Thereafter, while predetermined consumption electric power is applied to the heat source element HSE and the highest temperature is monitored and controlled, simulations are performed as to the heat distribution and heat gradient in the heat source element HSE and the space portion SP. Thereafter, the results of the simulations are analyzed. In the analysis, the highest temperature of the heat source element HSE, the temperature difference in the temperature sensing element TE, and the heat distribution and heat gradient in the space portion SP are studied. Thereafter, based on the results of the analysis, the area required to arrange the thermal protection circuit TSD in the space portion SP is determined, and finally the shape and size of the heat source element HSE and the space portion SP are determined. Through these steps, the area required in the heat source element HSE and the semiconductor device  10  suitable for the thermal protection circuit TSD to accomplish its function can be designed. 
         [0085]      FIG. 10  is a simulation diagram showing a relationship between electric power consumption and temperature detection sensitivity in the heat source element HSE. Specifically, it shows the results of heat distribution simulations that show the temperature difference between point P 1  and point P 4 , which is the central portion Tc of the temperature sensing element TE, at varying electric power consumption. As a parameter, two values were adopted, namely a configuration where, as shown in  FIGS. 5A to 5C , the lateral widths x 10  and x 20  of the opposing regions hse 10  and hse 20  equaled twice the lateral width x 30  of the coupling region hse 30  and a configuration where, as shown in  FIGS. 6A to 6C , the lateral widths x 12  and x 22  of the opposing regions hse 12  and hse 22  equaled three times the lateral width x 32  of the coupling region hse 32 . In both configurations, y 1 /y 0  equaled 0.5 and y 2 /y 0  equaled 0.5, and the space portion SP and the coupling region hse 30  (hse 32 ) had approximately the same size. 
         [0086]      FIGS. 5A to 5C ,  FIGS. 6A to 6C , and  FIGS. 7 to 9  thus far referred to deal with cases where the electric power consumption in the heat source element HSE was 30 W.  FIG. 10  is a characteristics diagram obtained from the results of heat distribution simulations when the electric power consumption was 30 W and 60 W. Along the horizontal axis is taken electric power consumption, and along the vertical axis is taken temperature difference. 
         [0087]    With the double lateral width, that is, with x 10  (x 20 )/x 30 =2, when the electric power consumption was 30 W, the temperature difference between points P 1  and P 4  was 44° C. Increasing the electric power consumption to 60 W with the other conditions unchanged caused the temperature difference to rise up to 88° C. 
         [0088]    On the other hand, with the triple lateral width, that is, with x 12  (x 22 )/x 32 =3, when the electric power consumption was 30 W, the temperature difference between points P 1  and P 4  was 22° C. Increasing the electric power consumption to 60 W with the other conditions unchanged caused the temperature difference to rise up to 48° C. However, it was found that, with the triple lateral width, the temperature difference between points P 1  and P 4  was far smaller than with the double lateral width. This suggests that, as a barometer that indicates the temperature detection sensitivity of the temperature sensing element TE, the ratio of the lateral width of the opposing regions (x 10 , x 20 , x 12 , x 22 ) to that of the coupling region (hse 30 , hse 32 ) matters greatly. 
         [0089]    The results of heat distribution simulations shown in  FIG. 10  are extremely useful in designing and manufacturing semiconductor devices and semiconductor integrated circuit devices of similar kinds. The reason is that the temperature detection sensitivity of the temperature sensing element TE for a wide range of electric power consumption by the heat source element HSE can be estimated. 
         [0090]    From  FIG. 10 , it is possible to estimate, for example, the temperature detection sensitivity of the temperature sensing element TE as will be obtained when the electric power consumption of the heat source element HSE is 5 W. It is seen that, when the lateral width of the opposing regions is twice that of the coupling region, the temperature difference is about 8° C. and, when the lateral width ratio is three times, the temperature difference is about 4° C. Thus, it is seen that, when the electric power consumption of the heat source element HSE is 5 W, the detection sensitivity of the temperature sensing element TE is 10° C. or less. It is also seen that, when the electric power consumption is 10 W, the temperature difference is about 16° C. and about 8° C. respectively. 
         [0091]    The characteristics diagram shown in  FIG. 10  varies depending on the thermal conductivity coefficient [W/m·° C.], density [kg/m 3 ], specific heat, etc. of so-called component materials such as the leadframe on which the semiconductor device  10  is mounted, the die-bonding material, the wire, the resin, etc. Thus, by previously preparing several combinations, it is possible to reduce the design period, and enhance the product quality, of the semiconductor device  10 . 
         [0092]      FIG. 11  shows an area ratio of the area of the heat source element HSE to that of the space portion SP, and is a diagram obtained by use, as parameters, of the entrance width (length x 3 ) and depth (length y 1 ) of the space portion SP and the widths (lengths x 1  and x 2 ) of the opposing regions hse 11  and hse 12 . 
         [0093]    In  FIG. 11 , for example, when x 1  (x 2 )/x 3 =2 and y 1 /y 0 =0.50, the area of the space portion SP equals one-ninth (=0.11) of that of the heat source element HSE, and thus the area ratio is 11.1%. This holds with  FIG. 5A . When x 1  (x 2 )/x 3 =3 and y 1 /y 0 =0.50, the area of the space portion SP is one-thirteenth of that of the heat source element, and thus the area ratio is 7.7%. This holds with  FIG. 6B . Although not illustrated in any diagram so far, when x 1  (x 2 )/x 3 =1 and y 1 /y 0 =0.75, the area of the space portion SP equals one-third of that of the heat source element HSE, and thus the area ratio is 33.3%. In the present invention, the proportion of the area of the space portion SP that occupies the area of the heat source element HSE is usually in the range from 3.7% to 33.3% shown in  FIG. 11 . That is, let the areas of the heat source element HSE and the space portion SP as seen in a plan view be S 1  and S 2  respectively, then S 2  falls largely in the range from 0.037×S 1  to 0.333×S 1 . 
         [0094]      FIG. 12  shows one example of a specific circuit configuration of the thermal protection circuit TSD arranged in the space portion SP. The thermal protection circuit TSD is of a well-known design. The thermal protection circuit TSD includes, in addition to the temperature sensing element TE, for example, constant current sources CC 1  and CC 2 , resistors R 1  and R 2 , a transistor Q, a comparator COM, and an inverter INV. As the temperature sensing element TE, for example, a diode-connected transistor is used. When the temperature sensing element TE is, for example, a diode, the forward voltage across the diode has a temperature coefficient of, for example, −2 mV with respect to variation in temperature. Thus, by subjecting the voltage occurring in the temperature sensing element TE to comparison by the comparator COM, it is possible to detect the temperature of the heat source element HSE. According to a TSD ON/OFF signal output from the comparator COM, the thermal protection circuit TSD is turned ON and OFF. As the temperature sensing element TE, a diffusion resistor, polysilicon resistor, or the like formed of a semiconductor can also be used. The thermal protection circuit TSD shown in  FIG. 12  is merely one example; its circuit configuration may be more complicate, with a higher degree of integration, or may be simpler. The entrance width and depth of the space portion SP can be determined according to the circuit configuration and the number of circuit components. 
       INDUSTRIAL APPLICABILITY 
       [0095]    With a semiconductor device and a method for designing one according to the present invention, it is possible, with a temperature sensing element, to detect a temperature that is close to the temperature of a heat source element based on heat distribution simulations. Thus, the present invention has extremely high industrial applicability, being suitable for use in semiconductor devices including power transistors, and for monitoring and controlling heat in semiconductor integrated circuit devices. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
         
           
               10  semiconductor device 
               11  first side 
               12  second side 
               13  third side 
               14  fourth side 
               15  fifth side 
               16  sixth side 
               17  seventh side 
               18  eighth side 
             CC 1 , CC 2  constant current source 
             COM comparator 
             HSE heat source element 
             hse 1 , hse 2 , hse 10 , hse 12 , hse 20 , hse 22  opposing region 
             hse 3 , hse 30 , hse 32  coupling region 
             OC other circuits 
             P 1  to P 5  point 
             Q transistor 
             SCH semiconductor chip 
             SP space portion 
             TE temperature sensing element 
             TSD thermal protection circuit