To enhance the solvent-resistance of polymer semiconductor film in organic field-effect transistors, bis(trichlorosily)hexane (BTH) as a cross-linkable agent was mixed with polymer semiconductors, poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2) and poly(3-hexylthiophene) (P3HT). The solvent-resistance was dramatically enhanced in both the F8T2/BTH and P3HT/BTH cases, even for the 1% addition of BTH. However, clear differences in the field-effect mobilities with increasing BTH-blend ratio were observed between the F8T2 and the P3HT cases. For the F8T2-FETs, the field-effect mobility was maintained by level of 90% at the 1% BTH-blend ratio, and decreased gradually above 1% blend ratio. In contrast, the field-effect mobilities of P3HT-FETs were dramatically decreased by blending the BTH, although the solvent-resistance was increased. This obvious difference is a result of the difference in crystalline properties between the amorphous F8T2 and the crystalline P3HT. This approach to improve the solvent-resistance of polymer films provides a facile method for the enhancement of the environmental stability in response to humidity and oxygen.