benchmark.cs

static readonly object s_lock = new object();
static readonly SemaphoreSlim s_semaphore = new SemaphoreSlim(1);
static int s_data;

[Benchmark]
public int Lock()
{
	lock (s_lock)
	{
		s_data++;
		return s_data;
	}
}

[Benchmark]
public int SemaphoreSync()
{
	try
	{
		s_semaphore.Wait();
		s_data++;
		return s_data;
	}
	finally
	{
		s_semaphore.Release();
	}
}

[Benchmark]
public async Task<int> SemaphoreAsync()
{
	try
	{
		await s_semaphore.WaitAsync().ConfigureAwait(false);
		s_data++;
		return s_data;
	}
	finally
	{
		s_semaphore.Release();
	}
}

results.md

.NET 5

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
Lock	18.67 ns	0.108 ns	0.101 ns	-	-	-	-
SemaphoreSync	45.94 ns	0.162 ns	0.144 ns	-	-	-	-
SemaphoreAsync	72.93 ns	1.446 ns	1.608 ns	0.0086	-	-	72 B

.NET 4.8

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
Lock	17.26 ns	0.084 ns	0.070 ns	-	-	-	-
SemaphoreSync	115.19 ns	1.456 ns	1.290 ns	-	-	-	-
SemaphoreAsync	180.12 ns	1.705 ns	1.595 ns	0.0126	-	-	80 B