A thermal flowmeter for measuring the flow rate of gas based on the amount of heat transfer from the gas to temperature-sensing resistors (6a, 6b, 7a, 7b), the flowmeter comprising: a substrate having a hollow space formed therethrough, a first insulating film deposited on the substrate in such a way as to cover the hollow space, a heat-generating resistor formed on the first insulating film, wherein temperature-sensing resistors (6a, 6b, 7a, 7b) arranged adjacent to the heat-generating resistor, electrodes arranged at an edge of the semiconductor substrate such that the electrodes are parallel to the edge in a longitudinal direction, and wiring for electrically connecting the electrodes and the heat-generating resistors, wherein the thermal resistance of a first area is almost equal to the thermal resistance of a second area, the first area being defined by a first side of the heat-generating resistor closer to the electrodes and by a first side of the hollow space closer to the electrodes, a second area being defined by a second side of the heat-generating resistor opposite the first side of the heat-generating resistor and by a second side of the hollow space opposite the first side of the hollow space so as to form a trapezoidal area, wherein the wiring extends from the first side of the heat-generating resistor toward the first side of the hollow space, wherein the thermal resistances of the first and second areas are controlled by adjusting the arrangement of the heat-generating resistor in a longitudinal direction, wherein the flow direction of the gas is in a lateral direction, wherein heat-generating resistor is arranged in the lateral direction at a center of the hollow space characterized in that: the arrangement of the heat-generating resistor in a longitudinal direction is such that L1 > L2, L1 being the distance from the first side of the heat-generating resistor to the first side of the hollow space, L2 being the distance from the second side of the heat-generating resistor to the second side of the hollow space, and wherein L1/L2 ≥ 1.5. a substrate having a hollow space formed therethrough, a first insulating film deposited on the substrate in such a way as to cover the hollow space, a heat-generating resistor formed on the first insulating film, wherein temperature-sensing resistors (6a, 6b, 7a, 7b) arranged adjacent to the heat-generating resistor, electrodes arranged at an edge of the semiconductor substrate such that the electrodes are parallel to the edge in a longitudinal direction, and wiring for electrically connecting the electrodes and the heat-generating resistors, wherein the thermal resistance of a first area is almost equal to the thermal resistance of a second area, the first area being defined by a first side of the heat-generating resistor closer to the electrodes and by a first side of the hollow space closer to the electrodes, a second area being defined by a second side of the heat-generating resistor opposite the first side of the heat-generating resistor and by a second side of the hollow space opposite the first side of the hollow space so as to form a trapezoidal area, wherein the wiring extends from the first side of the heat-generating resistor toward the first side of the hollow space, wherein the thermal resistances of the first and second areas are controlled by adjusting the arrangement of the heat-generating resistor in a longitudinal direction, wherein the flow direction of the gas is in a lateral direction, wherein heat-generating resistor is arranged in the lateral direction at a center of the hollow space characterized in that: the arrangement of the heat-generating resistor in a longitudinal direction is such that L1 > L2, L1 being the distance from the first side of the heat-generating resistor to the first side of the hollow space, L2 being the distance from the second side of the heat-generating resistor to the second side of the hollow space, and wherein L1/L2 ≥ 1.5.