Tungsten trioxide (WO₃) exhibits complementary optical and electrical responses toward hydrogen, yet the interplay between interfacial stress, crystal phase stabilization, and gasochromic/chemiresistive performance remains insufficiently understood. In this work, WO₃ films were grown on four single-crystal oxide substrates to systematically tune interfacial stress and thereby modulate the resulting crystal phase, microstructure, and exposed facets. θ–2θ diffraction revealed that WO₃ adopts a monoclinic phase on YAlO₃ and SrLaAlO₄, whereas a high-temperature orthorhombic phase is stabilized on LaAlO₃ (LAO) and SrTiO₃ due to stronger interfacial constraint. Compared with the amorphous quartz reference, the single-crystal substrates significantly enhanced both gasochromic and chemiresistive responses. In particular, the orthorhombic WO₃/LAO film exhibited an electrical response of 1.97 × 10⁴ (R_air/R_H2), an optical transmittance changed of 12.7%, and an electrical response time of 1 s toward 2% H₂ at 80 °C, far exceeding the monoclinic and amorphous counterparts. The combined effects of stress-induced phase stabilization, film orientation, and hydrogen diffusion pathways are shown to govern the non-monotonic sensing trends among different substrates. These findings elucidate the structural origin of hydrogen sensitivity in WO₃ and provide guidance for stress-engineered design of high-performance gasochromic and chemiresistive sensors.