Properties of electrolyte‐semiconductor barriers are described, with emphasis on germanium. The use of these barriers in localizing electrolytic etching is discussed. Other localization techniques are mentioned. Electrolytes for etching germanium and silicon are given.

Tables and charts are given of mathematical functions related to the potential of a line of point charges. The use of these functions is illustrated by applications to semiconductor resistivity measurements and to calculations of the base resistance of point‐contact transistors.

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PACS 01.65.+g, 82.45.Vp This paper recollects the research undertaken in the field of electrochemistry of semiconductors, leading to the discovery of porous silicon, some 50 years ago. Some of the attendees at the PSST-2004 were interested in the "time line" of related events. Original notebooks with actual dates were left in the care of Bell Telephone Laboratories. Carbon copies were not made and regularly filed (as done at some other research laboratories). Germanium point-contact transistorsThey were fabricated mostly on chemically-etched N-type germanium (P-type gave lower gain except at high frequencies). Electrolytic etching was considered as a process variation. Regions with a high density of chemical etch pits had already been correlated with low transistor yields. Electrolytic etching of the N-type material developed much larger pits along crystallographic directions in the N-type material. Micromachining of metals and semiconductorsRelocation of the work to a laboratory with a sink and drain somehow inspired an additional way to localize electrolytic etching and plating [3]. There was an intent to file for a patent. However, a "virtual cathode" configuration was discovered in a pre-1930 US patent. Dimensional analysis showed that "virtual electrode" processing can be more rapid, the smaller the size. The technique was applied by General Electric to make cooling holes in jet-engine turbine blade alloys. GE also advertised a hole-drilling service. Etching of silicon and germaniumWe then were given our first single crystal silicon. It was obviously not in demand for the NPN diffusedbase project, being P-type. That meant that we did not have to illuminate to provide holes. The stain now known as porous silicon was discovered on the first attempt to measure the "valence." Except for the unexpectedly low valence, the anode bubbles might have been assumed to be oxygen. The tendency of