OK, first, thanks for the reply.
I saw that DS18B20 during my search. But how do you mount it to the heat sink? I saw PT100 probes with an eyelet (I hope that´s translated correctly) with a diameter for M4 screws. That would be perfect because I could mount it under one of the heat sink screws. But I cant´t find a 1-wire probe with an eyelet.
From technical point the 1-wire probe would be perfect. But how do you connect them in series with one wire? You mean parallel, don´t you? So that all VDDs, all GNDs and all DQs are connected?
yes, the electrical connection is in parallel.
you can try some heat rezisting tape to glue it to the head sink. (this is what i have used).