This way...
select Deptid,Employeename,salary from
(
select row_number() over(order by e.did,salary desc) as srno,
did Deptid,e.EmployeeName,salary
from Empmaster e
JOIN Deptmaster d on e.did=d.deptid
group by did,e.EmployeeName
) as temp
where SrNo=1
Happy Coding!
:)