This chapter reviews the origin and characterization of electrically active deep level traps in GaN material and LED. In n-GaN, three levels E_C – 0.25 eV, E_C – 0.60 eV, and E_C – 0.90 eV are most commonly revealed by DLTS and E_C – 1.25 eV, E_C – 2.6 eV, and E_C – 3.28 eV are most commonly seen by DLOS. The levels E_C – 0.60 eV and E_C – 1.25 eV are dislocation-related levels. In GaN LED, DLOS is a more useful technique than DLTS because DLOS investigates near-mid gap levels in GaN. In fact, a combination of DLOS and lighted capacitance–voltage measurement realizes the defect density in each quantum well (QW) and quantum barrier (QB) of the GaN LED. Deep level traps within the first QW are highest in density.