LTC2498 Temperature Sensor Chip Code via SPI
Dont know if this will solve your problem but I would suggest you to do this change:

//CS des Thermochips auf low
PORTB &amp;= ~(1&lt;&lt;DD_SS);


Have you tried measuring with an oscilloscope?

Edit: Also noticed now that your comment syntax is a bit off, maybe problem when you pasted it to the forum? Does the code compile?

 masterIn = (result &amp; 0b00011111);  /*last 3 bits lost/* 


Should be:

masterIn = (result &amp; 0b00011111);  /*last 3 bits lost*/


And:

masterIn = (masterIn&gt;&gt;5) &amp; 0b00000000111111111111111111111111; /*Last 5 bits lost/* 


Should be:

masterIn = (masterIn&gt;&gt;5) &amp; 0b00000000111111111111111111111111; /*Last 5 bits lost*/