Semiconductor devices are decreasing in dimensions and currently comprise stacks of ultrathin layers as in a spin-transfer torque magnetoresistive random-access memory (STTMRAM) device. For successful characterization by transmission electron microscopy (TEM) for failure analysis and device development, an accurate and controllable thinning of TEM specimens for is desirable. In this work, we combine plan view Ga focused ion beam (FIB) and post-FIB Ar milling preparation to prepare TEM specimens from a STT-MRAM device. Post-FIB Ar milling technique as a final polishing step of plan view TEM specimens was shown to prevent exposure of the tunnel barrier layer that can be damaged by the Ga FIB beam. We discuss the plan view FIB preparation, post-FIB Ar milling step and image analysis of the TEM images.