A flat panel display device and a method of manufacturing the flat panel display device are disclosed. In one embodiment, the flat panel display device includes: i) a first substrate, ii) an active layer formed over the first substrate, wherein the active layer comprises a source region, a drain region, and a channel region, iii) a gate insulating layer formed on the active layer, iv) a gate electrode formed on the gate insulating layer and over the channel region of the active layer and v) a first interlayer insulating film formed on the gate insulating layer and the gate electrode. The device may further includes 1) a source electrode and a drain electrode electrically connected to the source region and the drain region of the active layer, respectively, through a contact hole, wherein the contact hole is formed in the first interlayer insulating film and the gate insulating layer, 2) a second interlayer insulating film interposed substantially only between i) the first interlayer insulating film and ii) the source electrode and the drain electrode, 3) a passivation layer formed on the first interlayer insulating film and the source electrode and the drain electrode and 4) a pixel electrode electrically connected to the source electrode or the drain electrode through a via-hole formed in the passivation layer.