Free: Contests & Raffles.
There is no restriction on using semi-auto handguns for hunting in modern season.
CP is right, also the barrel must be minimum of four inches and 24 cal or larger centerfire during modern season.
The regs do not have all of the laws in them and state that you need to look up the wac and educate yourself on the law without exception. However, having said that, the state shall make no law that contradicts the constitution. The trouble with that is you have to challenge the law of no sidearms during archery season. Good luck on spending all your resources taking this law all the way to the supreme court although you would have your name on it, "Palmer vs. THE STATE OF WASHINGTON."
I say carry the gun. I personally have found a pot grow operation during modern rifle season, and had I been hunting bow, I would have been facing off with drug growers. I would carry. Some laws are made to be broken (never thought i would hear myself say that ) but your personal defense trumps state law in my opinion...