High-performance thin-film transistors (TFTs) that use oxide semiconductors such as ZnO and amorphous InGaZnO (a-IGZO) are becoming an attractive alternative to hydrogenated amorphous silicon (a-Si:H) and organic-based materials because of their high electron mobility values and low processing temperatures, making them compatible with flexible substrates and opening the potential for low production costs. However, as with other TFT technologies, achieving long-term operational stability is also a major challenge faced by metal-oxide semiconductor TFTs. The degradation of the performance of a TFT during operation is reflected by changes of its current characteristics that can result from changes of mobility, threshold voltage or variations of the capacitance density. Here, we report on the fabrication of electrically stable amorphous InGaZnO TFTs that can be tuned to operate in either in depletion (D) or enhancement (E) mode without losing its electrical stability. The use of different annealing environments such as air, nitrogen (N2), and air/N2 with the control of the annealing temperatures leads to E- and D-mode operations of TFTs with high electrical stability showing less than 6% degradation of the drain currents after 1 hr direct current (DC) bias stress at a voltage of 8 V. In contrast, the current in an un-annealed TFT drops to 52% its initial value. These TFTs showed hysteresis-free voltage transfer characteristics with saturation mobility values of 7 ± 1 and 6 ± 1 cm2/Vs, and threshold voltage values of 2.0 ± 0.5 and -1.5 ± 0.5 for E- and D-mode TFTs, respectively. Here, we also demonstrate that high-gain inverters composed of electrically stable n-channel enhancement-mode (E-mode) and depletion-mode (D-mode) TFTs can be fabricated on a single substrate. As expected from the hysteresis-free current voltage characteristics, the inverters also show hysteresis-free voltage transfer characteristics (VTCs) with the maximum gain values of -62, -53, and -38 V/V at different VD = 8, 7, and 6 V with nearly constant switching threshold voltage (VM) value of 2.8 V. After electrical stress using multiple scans up to 500 cycles and 1 hr DC bias, VTCs of the inverters are slightly changed due to the small current variations of the a-IGZO TFTs. Here, the maximum static gain values at VD = 8, 7, and 6 V were -90, -82, and -52 V/V with VM of 2.5 V. Because p-channel metal-oxide TFTs are proven difficult to realize, the use of these electrically stable inverters based on electrically stable E-mode and D-mode a-IGZO TFTs could be an attractive alternative to conventional complementary metal-oxide technologies which require the use of a p-channel and an n-channel TFTs.