Aaron Bridgeman, 35, of Lansbury Park, had been racing a friend on a motorbike when Vicky Bridgeman fell from the back of the bike and was hit.
Bridgeman was found guilty of causing death by dangerous driving earlier this month.
Newport Crown Court heard he had been "driving at grossly excessive speed".
The court was told Bridgeman had never held a driving licence and how the weather on the day of the incident - 23 December, 2013 - "was atrocious", with weather warnings being issued by the Met Office.
Bridgeman and his friend Jason Szalkowski, 32, who had previously been disqualified from driving, decided to race on the narrow Pandy Lane, in Bedwas, the court heard.
He was driving his father's Peugeot while Mr Szalkowski was riding a Suzuki motorcycle with 40-year-old Ms Bridgeman - also known as Claire - as a pillion passenger.
After half a mile of racing, both Mr Szalkowski and Ms Bridgeman came off the motorbike, and Bridgeman, who was just half a second behind, drove into her.
A farmer, who was also using the road and witnessed the race, was unable to stop and also drove into Ms Bridgeman.
After the crash, Bridgeman asked the farmer if he was phoning 999. The court was then told he ran off, not knowing if his step sister was dead.
Ms Bridgeman died at the scene, the court heard.
Her step brother later handed himself into police.
At his trial, Bridgeman blamed the farmer for his step sister's death, but the jury found him guilty.
As well as the prison sentence, he was disqualified from driving for six years.
It was decided it was "not in the public interest" to prosecute Mr Szalkowski as he was so seriously injured in the crash.
A Caerphilly man who ran over and killed his step sister, while racing in his father's car, has been jailed for seven years.