This paper presents a fully-integrated stimulator chip for electrical microstimulation. The device is designed in a high-voltage process that allows up to 20V power supply and 19V output voltage compliance. A broad range of current-mode stimulation waveforms and patterns can be generated, including symmetrical/asymmetrical, biphasic/monophasic, and pulse train stimuli. The current amplitude, pulse width, and stimulation rate are adjustable from 0.5μA to 2mA, 100μs to 4ms, and 0.1Hz to 200Hz, respectively. Two complementary charge-balancing techniques are integrated to reduce residual voltage and stimulation artifacts. In in vitro experiments, the stimulator is demonstrated to trigger neural spikes, modulate neuronal firing rate, and alter mesoscopic neuronal activity. The results suggest the proposed microstimulator can support a wide variety of neuroscience experiments that require electrical microstimulation.