A transistor including a polysilicon layer on a base substrate and including a channel region, a first ion doping region, a second ion doping region, the channel region being between the first and second ion doping regions, an average size of the grains in the channel region being greater than that of the grains in the first and second ion doping regions, a first gate electrode insulated from and overlapping the channel region, a second gate electrode insulated from the first gate electrode and overlapping the channel region, an inter-insulating layer on the second gate electrode, a source electrode on the inter-insulating layer and connected to the first ion doping region, and a drain electrode on the inter-insulating layer and connected to the second ion doping region.