The 26-year-old from Sheffield had not dropped a game en-route to the last four at the National Squash Centre in 
Manchester - and was in devastating form as he despatched world number eight Barker 11-6, 11-5, 11-6 in 48 minutes.
"That's the best he's ever played against me," said the left-handed Londoner who upset Frenchman Gregory Gaultier, ranked two in the world, in the previous round. "And when you get beaten by a better player, it's somewhat easier to take."
After a historic day in which three Englishmen competed in the semi-finals for the first time in living memory, Matthew will face either fellow Yorkshireman James Willstrop, the former world number two, or Egypt's three-time world champion Amr Shabana in the final.
In the women's championship, Jenny Duncalf failed to reach the final for the second year in a row. The world number six from Harrogate went down 11-8, 11-7, 8-11, 11-6 to Rachael Grinham, the second-seeded Australian who is looking for her fourth title.
RESULTS: internationalSPORTgroup British Open Squash Championships, Manchester
Men's semi-final line-up:
[4] Nick Matthew (ENG) bt [6] Peter Barker (ENG) 11-6, 11-5, 11-6 (48m)
More to follow...
Women's semi-final line-up:
[2] Rachael Grinham (AUS) bt [4] Jenny Duncalf (ENG) 11-8, 11-7, 8-11, 11-6 (48m)
More to follow ....