Provided are a semiconductor device having small characteristic variations with time and high reliability and an in-vehicle control device using the same, the semiconductor device including a plurality of transistor elements constituting a current mirror circuit or a differential amplifier circuit that requires high relative accuracy. A semiconductor device includes a first metal-oxide-semiconductor (MOS) transistor, a second MOS transistor paired with the first MOS transistor, and insulation separation walls which insulate and separate elements from each other, wherein relative characteristics of the first MOS transistor and the second MOS transistor are in a predetermined range, the first MOS transistor and the second MOS transistor are relatively arranged in a gate width direction or a gate length direction, and distances between gate oxide films of the first MOS transistor and the second MOS transistor and the insulation separation walls facing the gate oxide films are the same as each other in a direction perpendicular to the gate width direction or the gate length direction.