An organic thin film transistor having an insulator layer formed of a polymer compound having a repeat unit represented by the following formula [1] is disclosed: ##STR00001## wherein R.sup.1, R.sup.2 and R.sup.3 are each independently a hydrogen atom or a methyl group, R.sup.4 is a hydrogen atom or a linear, branched or bridged cyclic hydrocarbon group having 1 to 12 carbon atoms, and x and y are molar ratio and are any number satisfying x +y=1, 0