Here, the effect of thermal annealing (TA) on the stability of solution-sheared thin films of the semiconducting polymer poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl)-alt-(2,2′;5′,2′’;5′’,2′’’-quaterthiophen-5,5′’’-diyl)] (PDPP4T) against the original coating solvent is studied, and it is shown that TA significantly improves the solvent resistance of semiconducting polymer films. Specifically, after the thin films are annealed at or above a critical temperature, the thin film thickness is largely retained when exposed to the original solvent, while for lower annealing temperatures material loss occurs, i.e., the thin film thickness is reduced due to rapid dissolution. The results of various techniques including grazing-incidence wide-angle x-ray scattering (GIWAXS), atomic force microscopy (AFM), and ultraviolet-visible-near infrared (UV–vis-NIR) absorption spectroscopy suggest physical changes as the cause for the increased solvent resistance. Such annealed films also show stable electrical characteristics in bottom-gate, top-contact (BGTC) organic field-effect transistors (OFETs) even after solvent exposure. In initial tests, a multitude of technologically relevant polymers show such behavior, underlining the potential impact of such temperature treatments for the fabrication of multi-layer polymer devices.