For the applications of two-dimensional (2D) semiconductors in future semiconductor technologies, several essential bottleneck problems are resolved. We develop an ion-bombardment and thermal annealing for repairing defects on surface of 2D semiconductors (such as PdTe2 and PtTe2), a high-speed switching of field-effect transistors (FETs) with ultrathin high-k Ta2O5 dielectrics, an extremely low-resistance contact technique with graphene and TaS2, low-temperature (250oC) epitaxy of h-AlN as dielectrics for gate-all-around field-effect transistors, and low-temperature (600oC) wafer-scale epitaxy of crystalline 2D semiconductors (WS2). These key advances push 2D semiconductors approaching feasible applications in future electronics.