Are people in Hawaii US citizens ?

Hawaii is a US state. Anyone born there is as much a citizen as anyone born in Alaska, Montana or Ohio.

Seriously, what part of Hawaii being a US state is not clear to you ?

Sheesh.

Hawaii has been a US possession since well before WWI, so anyone alive today who was born there is a citizen, even Barack Obama.  And Hawaii has been one of the states since 1959, before Obama was born there.  Obviously immigrants may not be.

Like any other state it depends.  Those born there are since Hawaii is a US State and under US law anyone born in the US has the right to US Citizenship.  Others who moved there from other countries may not be US Citizens at this time but are landed immigrants and may, or may not, be going through the citizenship process and I am certain there are even a few illegal immigrants there (mostly white by the way) who fall into no category.

Those who were born or naturalized in the US are citizens; and since HI is a state, anyone born in the state of HI are citizens.  

Some people are, and some people aren't.

Yes.  And no.  Really depends on the person

Some are and some aren’t. If they are born there then they are just like if they were born in any other US State or Territory or overseas to American parents. 

If they moved there from another country then they can become a US Citizen or they can remain a permanent resident. 

I am a citizen since I was born in the U.S. 

However, we have a number of immigrants who are legal residents. They are not citizens. (Though many of them have applied to become citizens.)

@Navycrab: " I had to renounce my other citizenship in order to get the Secret Clearance"... Bet you are playing with all the cool toys. As a former electrical engineer, I'm jealous. :-))

They have been since it became an American territory.

i think they could be