In this Letter, three-terminal transistor-based artificial synapses are proposed that are simply constructed with a solution-processed InOx channel and AlOx electrolyte gate. Paired pulse facilitation and short-term potentiation (STP) are realized and modulated by adjusting the amplitude, duration, and interval time of the spiking pulses. Furthermore, the STP is transferred to long-term potentiation (LTP) by increasing the pulse amplitude and number. In addition, spike-timing-dependent plasticity is demonstrated. The high density hydrogen in low temperature processed AlOx is adsorbed on InOx electrostatically or electrochemically, which plays a role in synaptic behaviors. This study provides useful information to understand neuromorphic devices based on solution processed oxide dielectrics and oxide semiconductors.