Multi-Chip Package (MCP) decapsulation is now becoming a rising problem. Because for traditional decapsulation method, acid can’t dissolve the top silicon die to expose the bottom die surface in MCP. It makes inspecting the bottom die in MCP is difficult. In this paper, a new MCP decapsulation technology combining mechanical polishing with chemical etching is introduced. This new technology can remove the top die quickly without damaging the bottom die using KOH and Tetra-Methyl Ammonium Hydroxide (TMAH). The technology process and relative application are presented. The factors that affect the KOH and TMAH etch rate are studied. The usage difference between the two etchant is discussed.