The mercury topped 31C in locations including Visp in the canton of Valais and Beznau in Aargau, according to the private weather channel meteonews.
Meanwhile, the magic 30C mark was reached in Geneva, Chur, and Schaffhausen. In Basel-Binningen, the maximum was 29.9C.
The hot weather on Wednesday came just before the start of the astronomical summer on Thursday.
While meteorologists use June 1st as their start point for summer, the astronomical summer in the northern hemisphere begins on June 21st.
This year it begins at 12.07pm precisely.
The astronomical summer will start with plenty of sunshine and with temperatures around 26C north of the Alps, although things are set to cool down considerably during the evening.
And while there will be plenty of sun in coming days, conditions will be milder according to government weather service MeteoSwiss (see the image above).