Unable to release Tempdb free space

Hi All,

My tempdb drive size is 50 GB. Now it is occupied 43 GB. when i checked sp_spaceused, the result as below.

database_name | database_size | unallocate space

tempdb               | 43161.94 MB   | 42953.48 MB

reserverd |  data | index_size | unused

1560 KB   | 688 KB | 712 KB     | 160 KB

when is tried to shrink, it is not releasing any space. there is no any active transaction.

can any one let me know why i am unable to release the space and also let me know how to release the space.?

Thanks & Regards

Krish