Crystalline Ga2O3 (c-Ga2O3) is a promising candidate for next-generation solar-blind photodetectors (SBPDs) but is suffering from high processing temperatures. Herein, seed-induced engineering is proposed via adopting Zn as an induced metal for crystallizing Ga2O3, lowering the processing temperature by 200 °C. After annealing, the Zn/Ga2O3 consists of an inner Ga2O3 layer of a monoclinic crystalline phase, top ZnO crystals coming from Zn oxidation, and a thin corundum Ga2O3 layer between them, which implies a "seed-induced" crystallization mechanism besides the nonequilibrium chaotic state caused by the traditional electron transfer one. As a result, the tailored c-Ga2O3 thin-film transistor-type SBPD with enhanced packing density and finite oxygen deficiency demonstrates a satisfactory responsivity of 8.6 A/W and also an ultrahigh UVC/visible rejection ratio (R254/R450) of 2 × 105. The seed-induced engineering forecasts its potential application in crystalline Ga2O3 SBPDs under a relatively low processing temperature.