Silicon Valley is an awesome comedy tv series (I actually think it's pretty underrated!). If you want to watch seasons 1-6 online for free then here are a few options (we checked these as recently as July 2020):
Amazon Video – All episodes (up to season 6) are available on Amazon Video, and you can sign up for HBO through Amazon Prime Video completely free in 10 seconds and have access to them immediately , plus a whole bunch of bonus content, 100% free!
Just cancel before the 7 days is up and you don’t pay a penny, simple. If you’re wanting to watch Silicon Valley for free and in high quality right now, then a free trial with HBO through Amazon Video is your best option.