New criterion for symmetric properties of defect potential in semiconductors is presented. For a degenerate energy level Es, we introduce the average Es of energy splitling under stress. Es is invariant under symmetry operation of Hamiltonian. Therefore, it is straight foward to reduce the stress coefficient tensor of Es by group theoretical method. For instance, for cubic semiconductors, if the defect level ET is withdefect potential of T group symmetry, the uniaxial stress coefficient of (?(Ec-ET))/(?F) or (?(ET-Ev))/(?F) is isotropic and equal to one third of corresponding hydrostatic pressurecoefficient. The case of defect potential with C3v symmetry is also discussed.The electron (or hole) emission and capture processes of defect levels under energy splitting are analysed. The weighted average of emission rate en and capture rate cn satisfy the following relation: en=gTgc-1cnN′ce(-(Bc-BT)/kT) By measuring the stress dependence of en., various schemes for determining the symmetry property of defect potential are discussed. The transient processes under defect level splitting are also discussed. When transitions are al lowed between the splitting states, the transient is exporential with single decay time constant en-1. When transitions between different states are forbidden, the transient is decay with multi-exponential time constants. en is determined by the initial transient slope.