A semiconductor integrated circuit device includes a power-supply terminal to which a power-supply voltage is input; and multiple MOS transistors including an Nch deplete mode MOS transistor functioning as a current source and at least one Pch enhancement mode MOS transistor formed on a silicon-on-insulator substrate including a silicon substrate, a buried-oxide film, and a silicon activate layer, each of the multiple MOS transistors dimensioned so that a bottom of a source diffusion layer and a bottom of a drain diffusion layer reach the buried-oxide film, the at least one Pch enhancement mode MOS transistor being connected to the supply terminal through the Nch depletion mode MOS transistor. The Nch depletion mode MOS transistor has electrical characteristics such that a source voltage thereof is higher than a silicon substrate voltage thereof and a saturation current of the Nch depletion mode MOS transistor is decreased.