Development of biologically inspired devices with artificial intelligence capabilities is critical for neuromorphic computing to break away from the current performance-limiting issues in a traditional von Neumann computing architecture. Optoelectronic synaptic devices, one of the biologically inspired neuromorphic devices, are attracting ever-increasing attention, but the active materials they contain restrict their practical applications. In this work, we demonstrate a simple, two-terminated, light-stimulated synaptic device based on GaN thin films due to their stable room-temperature persistent photoconductivity, large integration potential, and high compatibility with semiconductor technology. Such a GaN-based synaptic device has the capability of emulating multiple functionalities of biological synapses including the paired-pulse facilitation, the transition from short-term memory to long-term memory, and the cognitive behavior.