Serialization is the process of saving the state of an object into persistant medium.
BinaryFormatter class is used for serializing and deserializing an object.

HybridDictionary is optimized for key-based item retrieval from both small and large collections.

using System.Collections;
using System.Collections.Specialized; 
using System.IO; 
using System.Runtime.Serialization.Formatters.Binary;

HybridDictionary hd; 
FileStream fs; 
BinaryFormatter bf; 

private void Form1_Load(object sender, EventArgs e)
{
hd = new HybridDictionary(); 
hd.Add("Sh", "Shalvin"); 
hd.Add("Sa", "Saji"); 

foreach (DictionaryEntry de in hd) 
listBox1.Items.Add(de.Key + " " + de.Value); 

fs = new FileStream(@"c:\Sh.data", FileMode.Create); 
bf = new BinaryFormatter(); 
bf.Serialize(fs, hd); 
fs.Close();
}