This problem can be have multiples causes: fleas, bacterial infection, mycosis.
In such cases, the first thing that you need to do is treat your pet for fleas. Fleas are the most frequent cause for hotspot on dogs. You need to have treatment with anti inflammatory medicine to stop the scratching.
In addition you can try using itch relief shampoo (Hot Spots, Oatmeal shampoo,Aloe Vera shampoo) which will help for short periods of time.
You can also try using homeopathic products containing cedar wood oils, lavender and aloe vera .
There is also Resicort lotion (Virbac) which has antipruritic and anti-inflammatory action.
My advice is to go in for a vet consultation to find the cause for hotspot.