how to get the primary key based on data text field from drop down list in .net ver 4.0

protected void ddlload()
{
DataSet dataSet = new DataSet();
SqlConnection ddSqlConnection = new SqlConnection(sqlConnStr.ToString());

SqlCommand ddSqlCommand = new SqlCommand("SELECT Job_ID,Job_English_Name FROM [0004_Job_Tbl]", ddSqlConnection);
ddSqlCommand.Connection = ddSqlConnection;
ddSqlConnection.Open();
SqlDataAdapter da = new SqlDataAdapter(ddSqlCommand);
da.Fill(dataSet);
ddlJobDisplay.DataSource = dataSet.Tables[0];
ddlJobDisplay.DataTextField = "Job_English_Name";
ddlJobDisplay.DataValueField = "Job_ID";
ddlJobDisplay.DataBind();

ddSqlConnection.Close();

}