The laser beam induced current (LBIC) and the I-V test at liquid-nitrogen temperature were applied to characterize the PN junction region extension effect in the HgCdTe device processing. By LBIC and I-V test, it was found that the area of n-type region of p-type HgCdTe material implanted by Boron ion or etched by ion beam milling is larger than the nominal values. The transverse dimension of n-type region was measured. At the same time, it was found that the results obtained by both methods were comparable.