In typical injection molding processes, surface defects are often encountered, yielding products of inferior part quality. In an effort to identify and eliminate any unwanted finish, surface defects have been created consistently by injection molding and examined via the use of a new technique known as micro-thermal analysis ( muTA(TM)). muTA(TM) is an analytical form of microscopy that combines atomic force microscopy (AFM) and differential thermal analysis (DTA). The experiment was performed on polycarbonate/acrylonitrile-styrene-acrylate (PC/ASA) injection molded parts, using thermal probes. Surface defects, such as variations in gloss level, were produced on injection molded plaques by changing molding parameters including material temperature and packing pressure. muTA(TM) results reveal that rubber particle aggregation is one of the reasons for lowering the parts surface finish, also that scans performed at elevated temperatures, show that there were no changes in the polymer's multiphase morphology. Additionally, depth profiling by muTA(TM) established that PC and ASA are rich at the outermost surface of regions that possess a dull finish, whilst PC is the dominant material in regions of high gloss.