To realise a semiconductor device equipped with a high-voltage MISFET capable of forming a push-pull circuit on one chip by optimising a junction-separation structure. In the n-channel MOSFET (1), when a potential is applied to the gate electrode (15), to the source electrode (9), and across the drain electrode (5) and the semiconductor substrate (1a) to expand the depletion layer from the junction face of the semiconductor substrate (1a) and the well (3), the leading edge of this depletion layer does not reach the low-concentration drain diffusion region (4). When a potential is applied to the drain electrode (5), to the semiconductor substrate (1a), and across the source electrode (9) and the gate electrode (15) to expand the depletion layer from the junction face of the low-concentration drain diffusion region (4) and the well (3), and from the junction face of semiconductor substrate (1a) and the well (3), these depletion layers are connected with each other.