Monolayer transition metal dichalcogenides (TMDs) have drawn significant attention for their potential applications in electronics and optoelectronics. To achieve consistent electronic properties and high device yield, uniform large monolayer crystals are crucial. In this report, we describe the growth of high-quality and uniform monolayer WSe film using chemical vapor deposition on polycrystalline Au substrates. This method allows for the fabrication of continuous large-area WSe film with large-size domains. Additionally, a novel transfer-free method is used to fabricate field-effect transistors (FETs) based on the as-grown WSe. The exceptional metal/semiconductor interfaces achieved through this fabrication method result in monolayer WSe FETs with extraordinary electrical performance comparable to those with thermal deposition electrodes, with a high mobility of up to ≈62.95 cm V s at room temperature. In addition, the as-fabricated transfer-free devices can maintain their original performance after weeks without obvious device decay. The transfer-free WSe-based photodetectors exhibit prominent photoresponse with a high photoresponsivity of ~1.7 × 10 A W at V = 1 V and V = −60 V and a maximum detectivity value of ~1.2 × 10 Jones. Our study presents a robust pathway for the growth of high-quality monolayer TMDs thin films and large-scale device fabrication.