Abstract: CdZnTe (CZT) detector achieves excellent spatial and energy resolution in the broad energy range from 30 keV to 600 keV without cooling. Thus, CZT detector becomes a major detector used to research the field of X and γ-ray in space and astronomy. The present research concerns in the modified structure of discriminator grade planar CZT detector with the size of 10 mm×10 mm×5 mm and the development of large area detector composed of four individual 10 mm×10 mm×5 mm Frisch-grid CZT detector. Good linear energy response to ¹²⁵I, ²⁴¹Am, ⁵⁷Co, ¹³³Ba, ¹³⁷Cs γ-ray and good energy resolution for ¹³⁷Cs γ-ray were achieved for the developed large area CZT detector.