A display device with improved brightness and a method of controlling the display device are presented. The display device includes a driving transistor, a pixel electrode electrically connected to the driving transistor, a detecting transistor detecting a magnitude of an electric signal transferred from the driving transistor to the pixel electrode, and a controller. The controller regulates a data voltage applied to the pixel electrode based on a difference between the detected electric signal and a predetermined reference level. The display device achieves improved homogeneity of brightness by compensating for any deterioration of TFTs.