An integrated high temperature ultrasonic transducer (HTUT) sensor has been utilized for diagnosis of gas-assisted hot embossing process to fabricate V-cut patterns real-time, nonintrusively and nondestructively. The progression of the process, including plastic plate soften, gas introducing, cooling, and plate detachment inside the chamber, was clearly observed using ultrasound. Ultrasonic velocity could not only indicate the four steps of process, but also evaluate the replicating degree of the V-cut patterns on surface of plastic plate under various temperature and gas pressure settings. The experimental results indicate that the heights of V-cut patterns increase with temperature and gas pressure. POLYM. ENG. SCI., 53:2175-2182, 2013. (c) 2013 Society of Plastics Engineers