A method of fabricating a synaptic device is provided. The method includes forming a channel layer between a first terminal and a second terminal. The channel layer varies in resistance based on a magnesium concentration in the channel layer. The method further includes forming an electrolyte layer. The electrolyte layer includes a magnesium ion conductive material. A third terminal is formed over the electrolyte layer and applies a signal to the electrolyte layer and the channel layer.