Tessenberg (French: Montagne de Diesse or Plateau de Diesse) is an elevated plateau in Switzerland. It is located above Lake Biel, on the southern slopes of Chasseral, at an elevation of about 800 m. It is divided between the Swiss cantons of Bern and Neuchâtel, and three municipalities, Nods, Lignières and Plateau de Diesse.
The plateau is drained by Twannbach to the east and by Ruisseau de Vaux to the south-west, both emptying into Lake Biel, and as such part of the Aare basin.