Yes. You must have a written contract with your employer for a definite period. This contract must be signed by you and your employer. You must receive a copy of the contract.
A student contract is very important: it gives you security regarding your rights and obligations.
You can enter into a student contract for a maximum of 1 year. Once you have worked for an employer for longer than 1 year, your contract will be considered to be a normal labour contract. After that, you can no longer enter into a new student contract with that employer.
The contract must state a whole series of data.