In a series of electron-acoustic microscopic (EAM) studies on nondestructive internal observation of Si transistor-chips, we have reported; [I] change of the electron range (Re) and [II] use of phase images (PhIs). It was found by comparison of the methods that (a) an electron acoustic signal with intensity proportional to the energy-loss (EL) profile of the incident electron-beam is generated, (b) the profile of observable depth is analogous to the EL-profile, (c) the center of observation shifts deeper inside from the surface, and (d) when Phis are used, the effective range of the observable depth by EAM can be enlarged deeper than 60% of Re.