H1B transfer to New employer, When H1B extension is in pending stage

[Suresh Babu]

I am working in Company A and my h1b is valid till SEP 30th 2015. My current employer already filed the Extension but not yet received the approval notice. I just have the receipt number(status is "Case was received") which they filed for extension. Now, I got a offer from Company B and they can file my petetion in premium process.
But, my question here is, If Company B file my h1 process after SEP 30th 2015. Is it valid ? Because, I dont have approval notice of h1b extension.(I just have applied case number)
If company B file my H1 transfer after SEP 30th. Is it safe for me ? or Is there any risks in this case. ?

Thanks much in advance for your reply.

[shervin143]

Search and read about bridging petitions. If Company B files your petition after Sept 30th before your extension gets approved, then you fall under bridging category. In which case, company B's petition will not get approved until Company A's extension gets approved.