Provided is a semiconductor device which includes a semiconductor layer and an insulating layer adjacent to the semiconductor layer, in which the insulating layer is formed of a crosslinked product of a polymer compound that has a repeating unit (IA) represented by the following Formula (IA) and a repeating unit (IB) represented by the following Formula (IB); and an insulating layer-forming composition which is used for forming an insulating layer of a semiconductor device and contains a polymer compound that has the following repeating units (IA) and (IB). In Formulae, R1a and R1b each independently represent a hydrogen atom, a halogen atom, or an alkyl group. L1a, L2a, and L1b each independently represent a single bond or a linking group. X represents a crosslinkable group and YB represents a decomposable group or a hydrogen atom. m1a and m2a each independently represent an integer of 1 to 5. The symbol “*” represents a bonding position of the repeating units.