Scotsman Hall and English partner Mills, the 2010 winner, beat Englishman Oliver Leydon-Davis and Denmark's Lasse Moelhede 21-17 21-18.
The latter were off the back of winning last week's Norwegian International.
But Scottish number one Kieran Merrilees lost to Mark Caljouw in the last 16 of the singles, the Dutchman winning the deciding game 21-16.
Scotland's other quarter-final hopes, Rebekka Findlay and Caitlin Pringle, in the women's doubles bowed out 21-5 21-14 against Malaysia's Amelia Alicia Anscelly and Mei Xing Teoh.
Hall and Mills face Dutch pair Jelle Maas and Robin Tabeling in Saturday's semi-finals at Glasgow's Emirates Arena.
Hall said: "I have been coming to this tournament as a spectator, line judge and player since I was 17 and now we believe we can go on and win it.
"We want to win it - that's why we enter tournaments - and this is my home tournament and the crowd are great here."
Denmark remain in contention for all five titles, with 2014 champions Mathias Christiansen and David Daugaard facing Liao Kuan Hao and Lu Chia Pin of Chinese Taipei.
Having beaten Merrilees, Caljouw fell to Joo Ven Soong 21-19 9-21 21-11 and the Malaysian now faces Germany's Fabian Roth.
In the other semi-final, Anders Antonsen, at number two the highest ranked player left in the men's singles, meets Sweden's fourth seed Henri Hurskainen.
Women's top seed Natalia Koch Rohde lost to sixth seed Sabrina Jaquet 21-6 13-21 21-10 as the Swiss player prevented an all-Danish semi-final line-up.
She now faces fifth seed Mia Blichfeldt, while third seed Mette Poulsen and eighth seed Julie Finne-Ipsen will meet in the other semi-final.
Finne-Ipsen is also through to the last four of the women's doubles with Rikke Soby and Christiansen is still on course for two titles as he and Sara Thygesen are through to the mixed doubles semi-finals.
Britain's Adam Hall and Peter Mills have reached the semi-finals of the Scottish Open Grand Prix in Glasgow.