Year Foreign workers
1930 219.000
1931 155.000
1932 108.000
1933 148.000
1934 175.000
1935 188.000
1936 220.192
1937 265.689
1938 375.078
1939 939.386
1940 ?
1941 3.506.000
1942 4.665.000
1943 ?
1944 7.615.970
1945 ?

It should be noted that different sources state different number of workers during the war.

Sources used

Ulrich Herbert - Hitler's foreign workers