The carrier transport properties of lateral p + −n junctions composed of few-layer WS 0.3 Se 1.7 /(WO x )WS 0.3 Se 1.7 on thermally grown SiO 2 or high-κ amorphous Al 0.74 Ti 0.26 O y dielectric layers on p + -Si substrates were investigated and analyzed using field-effect transistor structures. Plasmalaser irradiation promoted selective oxidation near the few-layer WS 0.3 Se 1.7 surface and improved the rectification behavior of the current−voltage characteristics. A photocurrent current density (J ph ) of 4 × 10 −7 A/cm 2 was recorded for WS 0.3 Se 1.7 /(WO x )WS 0.3 Se 1.7 lateral p + −n junctions under simulated solar-light (AM1.5G) irradiation. Subsequently, improved J ph values of 7.1 × 10 −6 (∼17 times) and 1.23 × 10 −5 A/cm 2 (∼30 times) were obtained by inserting a silver (Ag) back-reflector layer between the amorphous Al 0.74 Ti 0.26 O y dielectric layer and p + -Si and an adding an antireflection (AR) layer of SnO 2 , respectively. In addition, an enhanced J ph of 1.3 × 10 −5 A/cm 2 was achieved with a V oc of 0.84 V and an FF of 57% upon applying a gate bias of +12 V. Thus, the photonic and electronic design of lateral p + −n junctions composed of few-layer WS 0.3 Se 1.7 /(WO x )WS 0.3 Se 1.7 structures contributes to further research on various types of 2D lateral heterostructures for the application in optoelectronic and photovoltaic devices.