<p>The performance of transistors based on two-dimensional transition metal dichalcogenide semiconductors is restricted by the poor interface quality between two-dimensional materials and conventional three-dimensional contacts. Transition-metal-dichalcogenide-based metal–semiconductor heterostructures have been developed to enhance device performance, but finding fabrication techniques that combine high-quality growth with scalability and broad applicability remains a challenge. Here we show that a method that combines metal–organic chemical vapour deposition and sulfurization can be used to create patterned heterostructures of niobium disulfide and molybdenum disulfide at the wafer scale. The niobium disulfide–molybdenum disulfide heterostructures can be used as the active channel material of field-effect transistors and non-volatile memory devices. Compared with pristine molybdenum disulfide, the heterostructures exhibit up to nine times higher on current due to a reduced contact resistance, a maximum effective mobility of 77 cm² V⁻¹ s⁻¹ and a 95.8% yield (of 144 field-effect transistors). Furthermore, our floating-gate field-effect transistors show a large programming window, precise and continuous conductance modulation, endurance over 60,000 programming pulses and an estimated retention time of around 19 years. Device simulation shows that the large programming window of the long-channel devices (around 14 V) can be maintained at scaled gate lengths below 100 nm with proper control oxide scaling.</p>