Fish, serving powerfully, defeated Lopez 6-3, 6-4 with the eighth-seeded Spaniard unable to reproduce the form that had seen him defeat compatriot Rafael Nadal, the world number one and French Open champion.
Earlier on Saturday, the 6ft 6in (1.98 metres) Querrey defeated Germany's Rainer Schuettler 6-7 (9/11), 7-5, 6-3.
The two American players share a coach, David Nainkin, and Fish said after his semi-final success that he was looking forward to playing Querrey in the final.
"Yeah, we are very good friends," said Fish. "We live close to each other in the States and we share the same coach. It will be fun.
"I haven't played him in three years. We'll probably put dinner on it or something, so it's a win win, at least."
Fish added: "I practise with Sam all the time almost when we're home. When we're all home together, it's almost every day. It shouldn't be a fairly new match-up for us."
Meanwhile, Querrey said: "He spends a lot of time in California and I do, too. We go out to dinner a lot. We're just really good buddies."
Querrey lost a close first set on a tie-break and did not earn a break point on the serve of former Australia Open finalist Schuettler until the 13th game of the second set.
But the big-serving 22-year-old then took charge.
A service break early in the final set saw Querrey heading to the final of an event that acts as a warm-up for Wimbledon, now the only one of tennis's four Majors played on grass.
This year's Queen's final will produce a suprise champion after a week of upsets that have seen defending champion Andy Murray, beaten by Fish, Andy Roddick, Novak Djokovic and Nadal all knocked out in south-west London.