Thin films of Y1Ba2Cu3O7−x(YBCO) with and without underlayers of SrTiO3(STO) were deposited via pulsed laser deposition onto substrates of sapphire and silicon‐on‐sapphire (SOS) in a single vacuum step. The YBCO films with STO underlayers displayed better superconducting transitions than the YBCO films without underlayers, with zero‐resistance temperatures of 86.5 and 75 K for films with underlayers on sapphire and SOS substrates, respectively. X‐ray diffraction and secondary‐ion mass spectroscopy have been used to explore the role played by the STO underlayer in improving film quality.