A solid state image pickup device, comprising an arrangement of a plurality of unit pixels each of which includes at least: a photodiode (17, 24, 25) for accumulating a signal charge generated by an incident light; and an amplifying MOS transistor (18, 19, 20) configured to receive the signal charge at a gate, to amplify the signal charge, and to output an amplified signal, wherein a source and a drain of the amplifying MOS transistor are disposed in a first semiconductor region of the first conductivity type which is the same conductivity type as the source and the drain of the amplifying MOS transistor, wherein the first semiconductor region has an impurity concentration lower than that of the source and the drain; a second semiconductor region of a second conductivity type opposite to a first conductivity type is disposed at least under a gate of the amplifying MOS transistor characterized in that said second semiconductor region is disposed in a deeper position than the source and the drain of the amplifying transistor (18, 19, 20) and on a position distant from the gate rather than the source and the drain of the amplifying MOS transistor; each unit pixel further including a third semiconductor region of the first conductivity type having an impurity concentration higher than the first semiconductor region and being disposed at an interface between a gate insulating film of the amplifying MOS transistor and a portion of the first semiconductor region forming a channel of the amplifying MOS transistor; and wherein the first semiconductor region has an impurity concentration such that, when driving an amplification operation of the amplifying MOS transistor, the first semiconductor region is depleted between the third semiconductor region and the second semiconductor region. a photodiode (17, 24, 25) for accumulating a signal charge generated by an incident light; and an amplifying MOS transistor (18, 19, 20) configured to receive the signal charge at a gate, to amplify the signal charge, and to output an amplified signal, wherein a source and a drain of the amplifying MOS transistor are disposed in a first semiconductor region of the first conductivity type which is the same conductivity type as the source and the drain of the amplifying MOS transistor, wherein the first semiconductor region has an impurity concentration lower than that of the source and the drain; a second semiconductor region of a second conductivity type opposite to a first conductivity type is disposed at least under a gate of the amplifying MOS transistor characterized in that said second semiconductor region is disposed in a deeper position than the source and the drain of the amplifying transistor (18, 19, 20) and on a position distant from the gate rather than the source and the drain of the amplifying MOS transistor; each unit pixel further including a third semiconductor region of the first conductivity type having an impurity concentration higher than the first semiconductor region and being disposed at an interface between a gate insulating film of the amplifying MOS transistor and a portion of the first semiconductor region forming a channel of the amplifying MOS transistor; and wherein the first semiconductor region has an impurity concentration such that, when driving an amplification operation of the amplifying MOS transistor, the first semiconductor region is depleted between the third semiconductor region and the second semiconductor region.