If you're trying to get a high security clearance job, what kind of background checks do they do on you?

Depends on the Security Clearance Level.

They check your background> Place of Birth, Date of Birth. Police Record.

Talk to your previous employers about what type of person you were when you worked for them.

Were your reliable.

Top Secret Clearance with Intelligence Material access. Then they start checking your family.

Where are your parents from > What country were they born in. Bothers and sisters...

For a TSC, they'll check a lot of stuff. Your criminal records, medical records, credit and financial records. They can even go as far as to asking your neighbors about you. Yes, they do check your family background. That's not to say that they'll check your 3rd cousin who lives on the other side of the country, but they'll check anyone you live with, your parents, siblings, etc.

You'd have access to classified information pertaining to national security. They don't just let anybody have that information, because it can be used against them if put in the wrong hands. They want to ensure that you're trustworthy and responsible before they let you know something like that.

However, few jobs require security clearances, especially a TSC.

For a secret clearance its a superficial look into you (your credit history, if you are a born citizen, criminal record etc.).

Top secret ones go deeper. They have investigators interview your friends, neighbors, family (extended too), your references, teachers, old class mates etc. They don't necessarily look into their backgrounds because they are not the ones under investigation. They just want "dirt" on you.

You and your family. In the early 1960's after I had been accepted into the USAF Aviation Cadets the FBI interviewed people who had been my family's neighbors as far back as when I was 4 years old.

GB

Major, Sqdn Cmdr, USAF, 1960-74

You and your family