How to maintain serial number for duplicate id in a table

Question

lets consider i have a table like this

create table #temp

(

Id int primary key identity(1,1),

amount decimal(10,0),

inserted_date datetime,

empId int,

series_no int

)

when i will insert record with empId 1000 ,then i want to insert serial no 1,2,3 for that employee id.

again if employee id 1001 then serial number start with 1,2,3 so on.. 

how could i achieve this any suggestion?