Multilayered structures of GeTe and Sb2Te3 phase change material, also referred to as interfacial phase change memory (iPCM), provide superior performance for nonvolatile electrical memory technology in which the atomically controlled structure plays an important role in memory operation. Here, we report on terahertz (THz) wave generation measurements. Three- and 20-layer iPCM samples were irradiated with a femtosecond laser, and the generated THz radiation was observed. The emitted THz pulse was found to be always p polarized independent of the polarization of the excitation pulse. Based on the polarization dependence as well as the flip of the THz field from photoexcited Sb2Te3 and Bi2Te3, the THz emission process can be attributed to the surge current flow due to the built-in surface depletion layer formed in p-type semiconducting iPCM materials.