The highest temperature – 38.6 degrees – was recorded in Rheinfelden, just across the Rhine River in Germany.
In many parts of German-speaking Switzerland and northern Graubünden temperatures were higher than at any point since the record summer of 2003, Daniel Gerstgrasser of weather service MeteoSchweiz told the Swiss news agency SDA.
The three-day heatwave reached its peak on Saturday.
In western Switzerland and the canton of Bern hailstorms and heavy rain set in on Sunday evening.
In the Bern region there were around 40 reports of flooded cellars, the cantonal police said, with local fire brigades called out to pump out water.
The police said they had received no reports of serious damage.
In Lugano, in the canton of Ticino, a group of 24 German hikers got into difficulties around 2,700 metres up in the Bedretto valley and had to be airlifted to safety by the air rescue service Rega.
A sudden storm and mist had prevented them from making any progress on the snow-covered path to the Corno-Gries hut.
The Germans were able to contact the hut attendant who called out rescuers at around 5pm.