I'm not a lawyer, nor an expert in this but I have seen this happening. In my opinion it all comes down to what the non-competition clause states in the contract. I've seen cases where it was as broad as "in the automation domain" and also very specific like "in the domain of EDA tools development". In the first case the judge might not even consider the clause because it is clearly a treat to your freedom (you cannot do anything else). In the second case you are pretty much tied to it.

Be careful because if you were working for an EDA company the defense can state that the semiconductor company (customer) hired you to develop the same automation tools internally (potentially saving them money in the future), and that's competition.

PS: I have a friend who recently got hired on a direct competitor of our company (EDA x EDA). Apparently he (and his lawyer) proved to the judge that he is working in a project that is completely different from what my company does, so far so good for him. But since the clause only works for a definite period time (1 year), he can potentially change to do whatever he wants after this time. So it also depends on how good your lawyer is.... Also, the company that hired him knew of the issue and is supporting him with its own lawyers.