This is really inaccurate. The real reason is similar to why America was at the forefront of the other high tech sectors like aviation etc too: massive defense spending, a lot of business people (like Fairchild) willing to invest in a sector where they see the potential procurement from Pentagon, while starting to serve the civilian sector.

This is very true.

The origin of the semiconductor industry of USA is in the WWII military research for microwave detectors used in radars.

The vacuum diodes were no longer useful at such high frequencies, so it was attempted to make better point-contact semiconductor diodes using germanium and silicon pure crystals, instead of using natural minerals, like galena, which had poor performance and were not reproducible.

Much of this WWII research and development effort has been done at the Bell labs. The most important results were the development of technologies for purifying germanium and silicon at levels never succeeded before for other chemical substances, for growing single crystals of Ge and Si, and for doping them in a controlled way with impurities.

Before WWII, all attempts to make semiconductor devices with good performances were unsuccessful, with the exception of a few applications that had very low performance requirements, like the AC rectifiers with selenium or copper oxide. The reason is that the properties of semiconductors are hugely influenced by even very small amounts of impurities or crystal defects.

Only by the end of WWII, with the availability of pure single crystals of germanium and silicon, which were the result of radar development during the war, the research on semiconductor devices could really start.

The experimental discovery of the point-contact transistor by Bardeen and Brattain was a direct product of the Bell team trying to find other applications for the technology of making point-contact diodes that was developed at Bell during the war. Then, stimulated by the experimental results, Shockley, who was an excellent theoretical physicist, developed a theory of the electrical conduction in semiconductors that has been the basis for the invention of the other semiconductor devices during the following decades. Shockley himself has invented several semiconductor devices using his theory, the very important BJT (bipolar junction transistor) and JFET (junction field-effect transistor) and the less important PNPN diode (a.k.a. Shockley diode).

The announcement of the transistor, which was "open-sourced" by the Bell Labs triggered intense efforts of R&D in semiconductor devices at many companies in USA and all over the world.

The very quick evolution of the semiconductor industry in USA and abroad during the first decades was determined by a complete disregard for what nowadays is called "IP".

ATT and the Bell Labs licensed the semiconductor technology cheaply to anyone and even gave it for free for certain purposes (e.g. for the purpose of making hearing aids, respecting the wishes of Alexander Graham Bell, the founder of ATT).

Then, in the following years, all advances in semiconductor devices and semiconductor technology were published with complete recipes of how to reproduce them. This ensured that all innovations spread immediately to all companies active in this domain. While significant inventions were patented, at that time patents were typically still licensed fairly and non-discriminatory, instead of being used as weapons against competitors.

The semiconductor and computer industries would have never flourished and something like the Silicon Valley would have never been created in the current environment of secrecy and paranoia about "protecting IP" and of abusing the patent and copyright laws to prevent competition and reach monopoly status.

To be fair, not protecting "IP" was the right strategy when the market for the semiconductor industry was growing, because the sharing of all knowledge ensured a much faster growth of the market, which was achieved both by replacing older technologies and by creating new applications enabled by the properties of the new devices. The growth of the market ensured that sharing was a win for each company.

In a stagnant market, a company can grow only if another shrinks, so a much more adversarial attitude is needed if growth is the goal, like weaponizing the "IP".