Thermally stable microstructured layers comprising polyurethane, polyurea and/or polyurethane/urea semi-IPN materials are provided which have microstructured surfaces which are highly durable, erosion resistant, and thermally stable. The microstructured layer comprises a semi-IPN of a polymer network selected from the group consisting of urethane acrylate polymer networks, urethane/urea acrylate polymer networks and urea acrylate polymer networks and a linear or branched polymer that is a thermoplastic polymer selected from the group consisting of thermoplastic polyurethanes, thermoplastic polyurethane/polyureas, thermoplastic polyureas, and combinations thereof. The microstructures are thermally stable at temperatures above the crossover point of the thermoplastic polymer, despite comprising a majority of such thermoplastic material. In another aspect, the present disclosure provides methods of making microstructured layers according to the present disclosure.