The number of semi skilled workers in an industry find themselves out of work, when improvements in technology render their jobs obsolete these workers experience?

Structural unemployment is the correct answer.

Explanation:

Because there is a large amount of the semi-skilled labors or workers in the industries and they find ourselves out of work because of the new technologies that execute their jobs by which those workers become obsolete. So, that's why these workers face the experience of structural unemployment which creates a higher rate of natural unemployment.