If there were some kind of interdiction on silicon (an evil genie or some kind of Butlerian Jihad perhaps?), the market would remember and/or rediscover the thermoelectric effect and throw money/postapocalyptic bartered goods at glassblowers pretty sharpish.
If that status continued, I'm sure we'd see developments in that space in terms of miniaturisation, robustness, efficiency, performance, etc., that would seem as improbable to us as a modern CPU would seem to someone in the no-silicon timeline. You may never get to "most of a teraflops in your pocket, runs all day on 4000mAh and costs three figures" but you could still do a meaningfully large amount of computation with valves.
