We present a methodology suitable for SEM and TEM analysis on Heterojunction Bipolar Transistors (HBT) developed for microwave applications. The Focused Ion Beam (FIB) technique has been investigated for SEM observations. It is found that best results are obtained when the active areas are micromachined from the back side and at a low incidence angle. The help of backscattered electron imaging for metallurgical assessment is emphasized on that kind of devices. A combination of both precision dimpling and FIB micromachining is found to be a good solution for the achievement of TEM slabs with an acceptable thickness. Finally we present the design of a dual beam system which uses Ar+ or Ga+ ions for highest TEM slab quality built into a SEM for an accurate localization and monitoring of the milling process. The respective advantages and limitations of this method are stressed in term of precision of localization of device features, surface roughness, contamination and slab thickness. The possibility to apply this technique on 0.1 µm silicon based technology will be discussed.