<TelerikDropDownList Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField" @bind-Value="selectedValue">
   <DropDownListSettings>
      <DropDownListPopupSettings Height="500px" />
   </DropDownListSettings>
</TelerikDropDownList>

@code {
public class MyDdlModel
   {
      public int MyValueField { get; set; }
      public string MyTextField { get; set; }
   }
int selectedValue { get; set; }
IEnumerable<MyDdlModel> myDdlData = Enumerable.Range(1, 20).Select(x => new 
MyDdlModel { MyTextField = "item " + x, MyValueField = x });
}