Abstract: A semiconductor device 100 includes an LDMOS transistor which includes: a P-type silicon substrate 102; a gate electrode 120 formed on the P-type silicon substrate 102; a drain (a second N-type diffusion area 109) formed apart from the gate electrode 120 in the horizontal direction; a drain electrode 130 formed on the drain (the second N-type diffusion area 109); an insulating film (a field oxide film 106) which is provided between the gate electrode 120 and the drain electrode 130, and has a film thickness thicker than that of a gate insulating film 112; and an electric field control electrode 118 formed along the drain electrode 130 on the insulating film.